THE INNERVATION OF THE HEAD AND NECK

The head and the neck serve as origins but also as passing ways for a number of important

nerves of the body. Obviously, some of these nerves are destined to provide the proper

innervation of the cephalic extremity. The innervation of the head and neck is alike to the

allover innervation of the human body, namely general sensitive, special sensorial, motor and

vegetative.

The general sensitive innervation acts for collecting the superficial sensitive (nociceptive,

thermal, tactile) information from the tegument and lining mucosae, the profound stretching

and pressure (proprioceptive) stimuli from some deeply situated somatic structures like

muscles, ligaments and articular capsules and the sensitive-vegetative innervation (visceral

pain and plenitude) of visceral and glandular organs. The first sensitive neuron (protoneuron)

is situated outside the neuraxis, grouped in the sensitive ganglia. The peripheral sensitive

fibers are more-or-less myelinated dendrites, originating from the peripheral sensitive ganglia.

The sensory (or special sensitive) afferent innervation is developed for some particular types

of stimuli, one single for each of the specialized organs of the senses: the olfaction for odors,

the sight for the light, the hearing for mechanic waves, the vestibular for the position and

movements of the head and the taste for soluble chemicals. The special sensitive afferents can

be of somatic (vision, hearing, equilibrium) or of visceral nature (olfaction, taste).

The motor innervation targets the generic somatic effector organs, the striated muscles.

According to their ontogenetic origin, the striated muscles and their motor innervation can be

somitic or branchial. Branchially derived muscles can be encountered exclusively on the head

and on the neck. It is to be mentioned, that some branchial striated muscles are located in

various visceral organs, thus they deserve visceral functions. The motor innervation of the

striated muscles or, at least the initiation of the movements is typically deliberate and well

sensed by the proprioceptive sensitive system. Movements are subject to highly effective,

feedback-based regulation mechanisms.

The vegetative innervation is particular to the vegetative effectors, smooth muscles and

glands. The vegetative motor and excretory functions are largely autonomous with almost no

sensitive feedback and with certainly no purposeful control of the conscience. Unlike the

somatic nerves, in addition to the intra-neuraxial centers, the autonomic nerves possess extra-

neuraxial relay stations, the vegetative ganglia (ganglion, Ggl.). The vegetative nerve fibers

(axons) originating from the centers emerge from the neuraxis as pre-ganglionar fibers, than

they synapse in a vegetative ganglion with the post-ganglionar (in fact: ganglionar) neuron,

wherefrom the post-ganglionar fiber (axon) originates. According to their neuromediators and

their final physiological action, the vegetative nerves can be of two types, sympathetic

(orthosympathetic) or parasympathetic. A vegetative effector organ, by its receptor apparatus

usually is responsive to only one of these two types of stimuli.

The peripheral nervous system (Systema nervosum periphericum) by the means of the

cranial nerves (Nn. craniales seu encephalici), a number of spinal nerves (Nervi spinales) and

the autonomous nervous system (Systema nervosum vegetativum seu autonomicum) serves as

the anatomical basis of all these types of innervation.

THE CRANIAL NERVES

The cranial nerves in fact are nerves originating from the brain stem, and accordingly, their

correct name would be encephalic nerves. Ancient anatomic studies described 12 pairs of

cranial nerves, and despite it is not the case, this numbering prevails. Actually, the first pair is

not a unitary cranial nerve and the second pair is not a cranial nerve, but an outgrown pathway

(tract) of the neuraxis. Moreover, there are two other pairs of peripheral nerves which could

be regarded as individual cranial nerves too: the terminal nerve (N. terminalis) and the

vomeronasal nerve (N.vomeronasalis), but they are not included in this group. According to

the tradition, the cranial nerves are numbered from above to below in the order they leave the

surface of the neuraxis.

Descriptively, a cranial nerve has its origin in a (or some) nucleus (nucleus, nuclei, Nc., Ncc.)

situated in the brain stem. This is the so-called proper origin of the cranial nerve, that in some

cases ( N.IV., N. VI., XII.) is unique, but in other cases (N.III., N.V., N. VII., N.VIII., N. IX., N.

X., N. XI.) is multiple. Following the proper origin, the cranial nerve emerges on the surface of

the brain, at the site of its apparent origin. The upper cranial nerves appear as unitary trunks,

but the N.V., N. VII., N. VIII., N. IX., N. X., N. XI., XII.) rise under the form of convergent

roots (Radix) or multiple radicular filaments (Fila radicularia) which merge in a trunk at a

distance of several mm from the surface of the medulla. The cranial nerves are paired and

symmetrical on the midline and they emit collateral branches and endbranches. Exception

from under this rule of symmetry is the N. X.

Topographically, the real encephalic nerves have their origin on the brain stem, in the

posterior fossa of the neurocranium (Fossa cranii post.). After their apparent origin, the

cranial nerves travel various distances on the inner skull base (Basis cranii interna) until they

reach the corresponding exit orifice of the neurocranium. On their intracranial way, the cranial

nerves are ensheathed by the leptomeninges, the pia mater and the arachnoidea. They also

establish clinically important topographic relationships (syntopy) with other intracranial

structures. When leaving the cranial cavity, they might exit straight away or they course quite

for a distance inside the cranial base until eventually showing up extracranially. Than the

cranial nerves continue their way to the target organs and structures, branch exhaustively and

develop elaborated syntopy. The branches can be collaterals (sidebranches) or terminal

(endbranches).

Systematically, a nucleus of a cranial nerve can be a nucleus of origin (Nc. originis) for

somatic motor and vegetative nerves, or nucleus of termination (Nc. terminationis) for

sensitive or sensory nerves.

Functionally, a cranial nerve can be purely motor, purely sensitive or mixed. Branchiomotor

and somitic motor functions never mix. There is no pure vegetative cranial nerve.

Endbranches of mixed cranial nerves are pure. It is important to understand that regardless to

their functional composition at their origin, on the periphery, in their tree, cranial nerves

frequently exchange branches, completing eachother’s effect. Usually some post-ganglionar

parasympathetic axons are swapped, and the typical accepting nerve is the N. V.

As for listing the cranial nerves, the anatomy uses roman numerals and/or proper names.

These, with the above-mentioned reserves are:

the N. I. or the olfactory nerve (Nn. olfactorii),

the N. II. or the optic nerve (N. opticus),

the N. III. or the oculomotor nerve (N. oculomotorius),

the N. IV. or the trochlear nerve (N. trochlearis),

the N. V. or the trigeminal (N. trigeminus),

the N. VI. or the abducent nerve (N. abducens),

the N. VII. or the intermediofacial nerve (N. intermediofacialis),

the N. VIII. or the vestibulocochlear nerve (N. vestibulocochlearis seu N. statoacusticus),

the N. IX. or the glossopharyngeal nerve (N. glossopharyngeus),

the N. X. or the vagal nerve (N. vagus),

the N. XI. or the accessory nerve (N. accessorius) and

the N. XII. or the hypoglossal nerve (N. hypoglossus).

The N. I. or the olfactory nerve (nerves) (Nn. olfactorii)

Despite from the view of the systematical anatomy they can be regarded as one single nerve

pair, descriptively the plural should be used. Systematically descirptively, the olfactory nerve

consists of approximately 20 slim bundles of axons penetrating into the cranial cavity. It is a

special visceral afferent nerve, as it conveys the olfactory information elicited by odoriferous

chemical compounds. The olfactory nerve in many ways is an exception from the usual

anatomy of the cranial nerves.

The proper origin is the first-order olfactory neuron (protoneuron), located inside the

olfactory region of the nasal mucosa (Tunica mucosa nasalis, Pars olfactoria). This neuron is

bipolar, and as an exception, with no intervening specialized receptor cell, it is directly

stimulated by the odoriferous chemicals. Thus, contrary to other visceral afferents, the fibers

of this nerve are not dendritic processes of sensitive ganglia, but unmyelinated axons.

The course of the nerves extracranially is hidden inside the olfacory mucosa, and then upon

approaching the cribriform plate of the ethmoid bone (Lamina cribrosa, Os ethmoidale) they

join each other in bundles of some 100 fibers each. About 20 such bundles are formed in this

way, and descriptively these are regarded as the proper olfactory nerves.

The olfactory nerves enter the neurocranium’s anterior fossa through the Foramina cribrosa.

As passing the cribriform foramina, each bundle gains its own internal pial and external dural

envelope, extensions of the intracranial meninges. These layers form a tight seal around the

axon bundles and fix them to the bony foramina, isolating the subdural, CSF-filled spaces

from the nasal cavity. When entered the anterior fossa of the neurocranium (Fossa cranii

ant.), the dural envelope enlarges and it is detached from the bundles, whereas the pial sheath

remains in a continuous solidarity until reaching the nerve’s apparent origin. The nerve fibers

then enter the olfactory bulb (Bulbus olfactorius). The olfactory nerve does not form a trunk,

nor does emit branches.

The apparent origin is the olfactory bulb. This lies just on the cribriform plate and it is

linked to the basal surface of the cerebral hemisphere by the means of a slender fascicle, the

olfactory tract (Tractus olfactorius). This latter, being an exposed neuraxial tract, is not to be

confused with the olfactory nerve.

The N. II. or the optic nerve (N. opticus)

By no means a nerve, it should be regarded an outdrawn tract of the diencephalon. It contains

the circa one million axons originating in the eyeball. However, given its position and course,

it is traditionally treated with the cranial nerves. Descriptively, the optic nerve is considered

that part of the optic pathways which is situated between the posterior surface of the eyeball

(Bulbus oculi) and the optic chiasm (Chiasma opticum) of the diencephalon. The tissue of the

optic nerve is built up by myelinated axons and it is populated by neuroglia, so that it equals

to the cerebral white matter. Thus, the term of optic nerve is purely descriptive.

The proper origin is in the eyeball, in the multipolar neurons of the nuclear layer of the

retina. Their axons converge toward the papilla of the optic nerve (Papilla nervi optici), pierce

the sclera and leave the eyeball.

The apparent origin is the optic disc, situated embedded in the sclera, somewhat medial to

the posterior pole of the eyeball.

The course is divided into four parts: intraocular, orbital, intracanalicular and intracranial.

During its run the optic nerve establishes important and complicated topographic

relationships. Meningeal layers, as extensions of the cerebral meninges envelope the nerve: an

outer dural sheath (Vagina externa nervi optici), inserting anterior on the sclera with whom it

merges, arachnoidea in the middle and pia mater on the neural surface (Vagina interna nervi

optici). The subdural space (Spatium intervaginale), filled with CSF is continuous along the

optic nerve up to the nerve’s origin from the sclera. The dural sheath tightly surrounds the

margins of the optic disc, thus the intracranial pressure is directly transmitted to the optic disc

and the intraocular papilla of the optic nerve.

The intraocular part (Pars intraocularis) of the nerve is the shortest, consisting of the axons

just transiting the layers of the eyeball. Here the axons form the optic disc, and this is

continuous with the optic nerve. The optic disc is pierced from posterior to anterior by the

central artery of the retina (A. centralis retinae). Beginning from the optic disc, the axons

acquire myelin sheath provided by oligodendroglia. The intraocular part is further divided in a

prelaminar (Pars prelaminaris), an intralaminar (Pars intralaminaris) and a postlaminar (Pars

postlaminaris) segments.

The orbital part (Pars orbitalis) of the nerve is the longest, of circa 25 mm. The nerve is

sinuous, being curved at first medially, then laterally. These windings provide an extra length

of the nerve, mandatory for avoiding its stretching during the rotational movements of the

eyeball. The nerve stretches towards the deepest point of the bony orbit (Apex orbitae), where

the optic canal (Canalis opticus) begins. The nerve and its sheaths are surrounded by the four

rectus muscles of the eyeball and the orbital fat pad (Corpus adiposum orbitae). 1 cm

posterior to the eyeball a branch of the ophthalmic artery (A. ophtalmica), the A. nervi optici

approaches of the nerve, perforates its sheaths, enters the neural white matter and travels in

the center of the nerve. Then, inside the optic disc this artery is continuous with the A.

centralis retinae.

The optic nerve enters the neurocranium’s middle fossa through the optic canal.

The intracanalicular part (Pars intracanalicularis) of the nerve is short, occurring as it passes

through the narrow optic canal (Canalis opticus) and leads from the orbit into the middle

cranial fossa (Fossa cranii media). The canal imposes the nerve a postero-medial direction.

Here the dural sheath is fixed to the upper and medial bony wall of the canal. At the posterior

end of the canal the ophthalmic artery (A. ophtalmica) lies infero-lateral to the nerve.

Advancing forward, the artery makes a quarter of turn around the nerve, going inferiorly and

then medially. As the canal can accommodate the nerve and the artery only, there is no

reserve space, thus the nerve is prone to damage already at the least of compression or space-

occupying lesion.

The intracranial part (Pars intracranialis) is of 10 mm in its length. It begins at the cranial

(posterior) opening of the optic canal and ends at the optic chiasm (Chiasma opticum). Here

the dural sheath suddenly enlarges and continues in the dural lining of the middle cranial

fossa. The nerve turns even more medially, approaches from lateral the prechiasmatic furrow

(Sulcus prechiasmatis) and ends by joining the diencephalon. There is no clear-cut limit

between the optic nerve and the chiasma.

Naturally, in the case of the optic nerve there is no question of forming a nervous trunk or

emitting branches.

The N. III. or the oculomotor nerve (N. oculomotorius)

Functionally, this is a mixed somitic motor and vegetative parasympathetic efferent

encephalic nerve with some proprioceptive sensitive component hosted in its endbranches. It

is the thickest of the optomotor nerves (oculomotor, trochlear, abducent).

Its somitic somatomotor branches are axons which innervate some of the extrinsic muscles

of the eye and the elevator muscle of the upper eyelid, as follows:

the medial rectus (M. rectus medialis bulbi),

the superior rectus (M. rectus superior bulbi),

the inferior rectus (M. rectus inferior bulbi),

the inferior oblique (M. obliquus inferior bulbi) and

the elevator of the upper eyelid (M. levator palpebrae superioris)

Its autonomous division consists of vegetative motor parasympathetic preganglionar axons.

This component leaves the nerve in the orbit and joins some of the branches of the trigeminal

nerve, and via the trigeminal branches innervates some of the intrinsic muscles of the eyeball,

as follows:

the constrictor of the iris (M. sphincter pupillae seu M. constrictor pupillae) and

the circular muscles of the ciliary body (Fibrae circulares, M. ciliaris)

The proprioceptive component is only present at the very periphery of the axonal tree. It is

represented by a few dendritic fibers, which soon pass as communicating branches where they

truly belong, into the trigeminal system.

The proper origin lies in the midbrain (Mesencephalon) and it is multiple:

the Nc. n.-i oculomotorii - somatomotor for the extrinsic ocular muscles,

the Nc. centralis (of PERLIA) - somatomotor for the elevator of the upper eyelid and

the Nc. accessorius (of EDINGER – WESTPHAL) - vegetative parasympathetic, origin for the

preganglionar vegetative axons

The apparent origin is the on the ventral surface of the neuraxis, on the mesencephalon, in

the interpeduncular fossa (Fossa interpeduncularis), lateral to the posterior perforated

substance (Substantia perforata post.), medial to the cerebral peduncles (Pedunculus cerebri).

The course of the nerve on the inner skull base is quite lengthy. It passes through the

interpeduncular cistern (Cisterna interpeduncularis) enveloped by its own pial sheath,

between the superior cerebellar artery (A. cerebellaris sup.) and the posterior cerebral artery

(A. cerebri post.). The nerve then pierces the dura lateral to the dorsum sellae and below the

posterior clinoid process (Processus clinoideus post.) and enters the cavernous sinus (Sinus

cavernosus). In the cavernous sinus the nerve runs under the internal carotid artery (A. carotis

int.), and on descent crosses the vessel’s lateral surface.

The oculomotor nerve exits the neurocranium’s middle fossa through the superior orbital

fissure (Fissura orbitalis sup.).

Further, it stretches medial and then below to the ophthalmic (N. ophtalmicus), trochlear and

abducent nerves. Inside the cavernous sinus the oculomotor nerve emits its two terminal

branches.

Branches: the nerve gives rise to no collaterals, instead in the anterior part of the cavernous

sinus splits into two endbranches. These are the superior and the inferior branch, as follows:

The superior branch (R. superior) is the weaker one. Exits the cavernous sinus and becomes

evident under the lesser wing of the sphenoid (Ala minor ossis sphenoidalis). It transits the

superior orbital fissure (Fissura orbitalis sup.), enters the orbit. Further, it passes through the

tendinous ring (Anulus tendineus) of the extrinsic ocular muscles, lateral and then superior to

the optic nerve and the ophthalmic artery, arriving on the lower surface of the superior rectus

muscle. There it branches exhaustively for the M. rectus superior and the M. levator

palpebrae superioris.

The inferior branch (R. inferior) is thicker. Likewise, it leaves the cavernous sinus,

penetrates the orbit through the superior orbital fissure. The nerve passes the inferior part of

the tendinous ring, medial to the abducens nerve. Gaining on the upper surface of the M.

rectus inf. it gives off two short branches for this one and for the M. rectus med. A longer

terminal branch stretches further inferior to innervate the M. obliquus inf., but this is the one

carrying the vegetative component too. The vegetative motor fibers leave this branch and

enter the ciliary ganglion (Ggl. ciliare) as the preganglionar root of this ganglion (Radix

parasympathetica).

Delicate, sparse connections emerge from the above described motor branches and unite with

twigs of the ophtalmic nerve. These are proprioceptive sensitive dendrites, proper of the

trigeminal system, dispatched from here via the motor nerves into the extrinsic ocular

muscles.

The ciliary ganglion (Ggl. ciliare) is a small peripheral nervous structure situated in the orbit,

behind the eyeball, lateral to the optic nerve, medial to the M. rectus lat. bulbi. This ganglion

houses the ganglionar („postganglionar”) neurons of the vegetative parasympathetic division

of the oculomotor nerve. It is morphologically linked by the means of roots and branches to

the oculomotor, the trigeminal and the sympathetic nervous trees, but functionally and

systematically belongs to the oculomotor system only. According to ARNOLD’s rule, from the

point of view of the systematic anatomy, as the cephalic parasympathetic ganglia generically,

the ciliary ganglion has three roots and one set of branches. Out of the three roots one is real,

with functional value, the other two are spurious.

The parasympathetic root (Radix parasympathetica seu oculomotoria), conveying the

preganglionar axons, is the only proper root of the ganglion, originating in the Nc. accessorius

(of EDINGER – WESTPHAL). This emerges from the inferior branch of the oculomotor nerve.

The preganglionar axons synapse on the ganglionar cells, which emit postganglionar axons

representing the output of the ciliary ganglion.

The sympathetic root (Radix sympathetica) only apparently belongs to the ganglion, because,

in fact, these axons merely transit it. Their origin resides in the superior cervical ganglion

(Ggl. cervicale sup.) of the cervical sympathetic chain, and they approach this ganglion via

the nervous plexus surrounding the internal carotid artery (Plexus caroticus internus) and its

continuation, the Plexus ophtalmicus. The fibers pass the ciliary ganglion without making any

functional connection with it and join the vegetative branches emerging from here, the short

ciliary nerves (Nn. ciliares breves).

The sensitive root (Radix sensitiva) is a trigeminal branch, passing through, but functionally

not linked to the ganglion. It originates from the nasociliary nerve (N. nasociliaris), a branch

of the ophthalmic nerve (N. ophtalmicus), which in turn is a primary branch of the trigeminal

nerve (N. trigeminus). Up to the ciliary ganglion this nerve is purely sensitive, built up by

some peripheral dendrites dispatched from the trigeminal sensitive ganglion (Ggl.

trigeminale). Obviously, these fibers do not synapse in the ciliary ganglion; instead they

directly enroll into its vegetative output.

The emerging branches of the ciliary ganglion are the short ciliary nerves (Nn. ciliares

breves), in a number of 8-10. They contain the postganglionar parasympathetic axons

originating in the ciliary ganglion, other postganglionar sympathetic axons just transiting it

and general somatic sensitive dendrites from the trigeminal system. These thin nerves then

penetrate the eyeball through its posterior pole and provide the motor innervation of the

intrinsic, smooth intraocular muscles.

The N. IV. or the trochlear nerve (N. trochlearis)

The trochlear nerve is a somitic somatomotor efferent encephalic nerve with the appearance of

a slender bundle. It is unique among the encephalic nerves by the facts that contains

intraneuraxially crossed fibers and arises on the posterior surface of the neuraxis.

It only innervates the superior oblique muscle of the eye (M. obliquus superior bulbi).

The proper origin lies in the mesencephalon, in the trochlear nucleus (Nc. nervi trochlearis).

From their origin, the axons turn posterior and decussate through the midline in the white

matter of the Velum medullare superius, part of the mesencephalic tectum (Tectum

mesencephali).

The apparent origin is to be found on the Velum medullare sup., below the inferior colliculi

(Colliculus inf.), nearby to the midline.

The course of the intracranial segment of the nerve begins with a half a turn around the

cerebral peduncles (Pedunculus cerebri), right above the superior border of the pons. As the

nerve encircles the posterior, then lateral surface of the mesencephalon, it passes the Cisterna

ambiens and then the pontine cistern (Cisterna pontis). On the lateral surface of the brain the

nerve stretches between the superior cerebellar artery (A. cerebellaris sup.) and the posterior

cerebral artery (A. cerebri post.) and pierces the dura mater near the medial, free margin of the

tentorium (Tentorium cerebelli), little above the trigeminal nerve, and penetrates the

cavernous sinus (Sinus cavernosus). Here the nerve runs anteriorly along the ophthalmic

nerve, above the abducent nerve. Then it leaves the cavernous sinus, shows up in the middle

cranial fossa, then disappears under he lesser wing (Ala minor) of the sphenoid bone.

The trochlear nerve exits the neurocranium’s middle fossa by passing through the superior

orbital fissure (Fissura orbitalis sup.).

In the orbit the nerve is placed above the origin of the levator palpebrae superioris muscle and

stretches forward and medially to meet from above its target, the superior oblique muscle of

the eye (M. obliquus sup. bulbi).

The trochlear nerve does not emit branches.

The N. V. or the trigeminal nerve (N. trigeminus)

The trigeminal nerve is a branchial somatomotor efferent and general somatic sensitive

afferent encephalic nerve. Its endbranches are joined by twigs of other cranial nerves with

different functions. It is unique among the encephalic nerves by the fact that it does not form a

nervous trunk, instead its primary branches emerge directly from its sensitive ganglion.

Therefore, the concept of „trigeminal nerve” is a systematic and functional one, rather than

descriptive or topographic. Despite that the very distal branches of the nerve gather with

vegetative axons of different provenances, in its central and proximal parts the trigeminal

nerve has no vegetative component.

The branchial somatomotor division consists of axons from the motor nucleus and provides

the innervation of the striated muscles derived from the I. branchial arch (Arcus branchialis

I.). These are the gnathomotor muscles and some smaller muscles too, as follows:

the temporal muscle (M. temporalis),

the lateral pterygoid muscle (M. pterygoideus lat.),

the medial pterygoid muscle (M. pterygoideus med.),

the masseter muscle (M. masseter),

the anterior belly of the digastric muscle (M. digastricus, Venter ant.),

the mylohyoid muscle (M. mylohyoideus),

the tensor tympani muscle (M. tensor tympani) and

the tensor veli palatini muscle (M. tensor veli palatini).

The general sensitive function is fulfilled by means of the peripheral dendrites of the nervous

tree with their origin in the sensitive ganglion (Ggl. trigeminale seu semilunare) (of GASSER)

and the sensitive root of the nerve (Radix sensitiva seu Portio major).

The trigeminal nerve provides nociceptive innervation for the teguments of the head, the oral,

ocular and nasal mucosae, the dental arches, paranasal sinuses, the eyeball and the content of

the orbit, the meninges of the anterior and middle cranial fossae, the muscles of the head and

chin and the TMJ (Art. temporomandibularis).

The trigeminal nerve is protopathic and epicritic tactile by innervating the cephalic teguments,

mucosae and mainly the tongue (Lingua).

The trigeminal nerve supplies proprioceptive innervation for all the muscles located on the

head (gnathomotor, Diaphragma oris, ocular, facial and auricular), the tongue, the dental

arches and the TMJ.

The somatomotor function is exerted by the means of the efferent axons originating in the

pons, which at first run separately, then join a primary sensitive branch of the nerve, the N.

mandibularis, and directly innervate the target muscles.

The proper origin lies in four nuclei.

the Nc. tractus mesencephalici nervi trigemini – proprioceptive, actually a centrally migrated

peripheral ganglion, in the mesencephalon,

the Nc. motorius nervi trigemini (Nc. masticatorius) – origin of the somatomotor efferences,

in the pons,

the Nc. sensitivus principalis – epicritic tactile and conscious proprioceptive, in the pons and

the Nc. tractus spinalis nervi trigemini – nociceptive, in the medulla, descending into the

spinal chord, in the first 2-3 cervical segments.

The axons originating in the motor nucleus form a single bundle and will emerge separately to

the sensitive nerve fibers. The sensitive axons, originating in the trigeminal ganglion enter the

brainstem forming a single bundle with the proprioceptive sensitive dendrites which leave the

brainstem.

The apparent origin is to be found medially on the ventrolateral surface of the middle

cerebellar peduncle (Pedunculus cerebellaris medius), at their junction with the pons in the

form of two emergent white bundles, the two roots of the trigeminal nerve. The medial one is

the thinner motor root (Radix motoria seu Portio minor). The thicker lateral root is the

sensitive (Radix sensitiva seu Portio major). In fact, the motor root, as its structure and

systematic anatomy does not change during its run, could be considered a separate motor

nerve by itself.

The course of the intracranial segment of the nerve is marked by the fact that unlike in the

case of the other encephalic nerves, the two roots, motor and sensitive, do not merge into a

unitary nervous trunk. They have separate pial envelopes but a common arachnoid sheath. The

roots, keeping close, advance and ascend laterally in the pontine cistern (Cisterna pontis).

They then pierce together the basal dura mater just below the insertion of the tentorium. After

a run of 1 cm, the roots penetrate a duplication of the basal dura mater, the Cavum trigeminale

(of MECKEL). The trigeminal cavum is pocket-like, with an upper and a lower wall, and rests

in the Impressio trigeminalis, a shallow pit of the petrous part of the temporal bone (Pars

petrosa ossis temporalis), just lateral to its apex.

Inside the trigeminal cavity the sensitive root meets a flattened, crescent-shaped ganglion and

fuses with its concavity. This is the peripheral sensitive ganglion of the trigeminal nerve (Ggl.

trigeminale seu semilunare) (of GASSER). The lesser motor root passes under the ganglion

with no functional connection with it. Medial to the ganglion lays the cavernous sinus (Sinus

cavernosus) with the internal carotid artery inside, inferior to it stretch medially the two

petrosal nerves, toward the foramen lacerum.

The primary branches of the trigeminal nerve are its endbranches too: the ophthalmic nerve,

the maxillary nerve and the mandibular nerve. These all separate from the convexity of the

trigeminal ganglion. A trigeminal nerve, as a descriptive anatomical entity actually never

forms, because the main branches emerge directly from the sensitive ganglion. The primary

branches are short as they soon separate in their own endbranches. Next, these branches are

treated in the same manner as the individual encephalic nerves are.

The ophthalmic nerve (N. ophtalmicus)(V/1) is the first branch of the trigeminal nerve. It is

the thinnest, medial division. At its origin the nerve is purely somatosensitive, formed by

sensitive dendrites, originating in the trigeminal ganglion (nociceptive and tactile) or in the

Nc. tractus mesencephalici nervi trigemini (proprioceptive). The nerve provides sensitive

innervation for the content of the orbit, the skin of the eyelids (Palpebra) and forehead, for the

meninges in the anterior and the middle cranial fossae, for the nasal mucosa (Mucosa nasalis)

and the skin of the nasal pyramid (Pyramis nasi). However, some of its most distal branches

are parasitized by vegetative postganglionar axons of different provenance. Likewise, the

nerve cedes some proprioceptive dendrites to the nerves innervating the extrinsic ocular

muscles. Apparently, these dendrites are taken over from the motor nerves.

Immediately after its origin, the nerve enters the cavernous sinus (Sinus cavernosus). There

the ophthalmic nerve courses anteriorly, at first below and then lateral to the trochlear,

oculomotor and abducent nerves. After exiting the cavernous sinus at its anterior border, the

ophthalmic nerve becomes apparent for a short while in the middle cranial fossa. Here the

nerve emits a collateral branch and after that it splits in three endbranches.

The trifurcation of the nerve happens in the middle cranial fossa, under the lesser sphenoid

wing (Ala minor ossis sphenoidalis), thus in the view of the descriptive anatomy the

ophthalmic nerve does not enter the orbit. Systematically regarded, the nerve is present in the

orbit by its branches, as follows:

R. tentoris (R. meningeus) – the only collateral branch of the ophthalmic nerve and does not

leave the cranial cavity. It turns posterior and medial for providing the sensitive innervation of

the tentorium and the posterior part of the falx (Falx cerebri).

The lacrimal nerve (N. lacrimalis) is the lateral endbranch of the nerve. Its origin is in the

middle cranial fossa, and then passes the superior orbital fissure through its lateralmost part.

Gaining into the orbit it maintains its anterior course, keeping laterally along the upper margin

of the lateral rectus muscle of the eyeball. It pierces the lacrimal gland (Glandula lacrimalis)

and branches exhaustively at the upper eyelid (Palpebra sup.) in its lateral part. These

endbranches serve for the sensitive innervation of the skin of the lateral angle of the eye and

the lateral conjunctiva (Angulus palpebralis lat.). On its way, the lacrimal nerve establishes a

functionally important communication with the zygomatic nerve (N. zygomaticus), the Ramus

communicans cum nervo zygomatico. By this bundle postganglionar parasympathetic axons

are transferred to the lacrimal nerve. These axons arrive from the pterygopalatine ganglion

(Ggl. pterygopalatinum), functionally belong to the system of the intermedius nerve (N.

intermedius) and supply the lacrimal gland (Glandula lacrimalis).

The frontal nerve (N. frontalis) is the strongest, middle endbranch of the ophthalmic nerve. It

also enters the orbit through the middle part of the superior orbital fissure and advances on the

elevator muscle of the upper eyelid under the ceiling of the orbit. It ends without emitting

collateral branches, by bifurcation into the supraorbital nerve, lateral, and the supratochlear

nerve, medial.

The supraorbital nerve (N. supraorbitalis) leaves the orbit through the supraorbital notch or

foramen (Incisura seu Foramen supraorbitale). It splits into two endbranches, the R. med. and

the R. lat. They ascend parallel in the skin of the forehead providing its general sensitive

innervation up to the vertex (Vertex).

The supratrochlear nerve (N. supratrochlearis) exits the orbit above the trochlea of the

superior oblique muscle of the eyeball (Trochlea m.-li obliqui superioris) and fits into the

supratrochlear notch or foramen (Incisura seu Foramen supratrochleare). It runs long in the

skin of the forehead, innervating it, but also provides branches for the skin and conjunctiva of

the interior angle of the eye (Angulus palpebralis med.).

The nasociliary nerve (N. nasociliaris) is the medial endbranch of the ophthalmic nerve. The

nerve passes the superior orbital fissure in its medial part and enters the orbit through the

tendinous ring of the extrinsic ocular muscles, above the optic nerve. It advances below the

superior oblique muscle of the eyeball, and then follows the medial wall of the orbit, joining

the ophthalmic artery up to the anterior ethmoidal foramen (Foramen ethmoidale ant.). There

the nerve bifurcates, but before that gives off several collateral branches. This nerve has

apparent anatomical connections with the ciliary ganglion. (see at the oculomotor nerve)

The R. communicans cum ganglione ciliari is a collateral branch of the nasociliary nerve. It

can be multiple, stretching anterior, lateral to the optic nerve. This nerve is the spurious

sensitive root of the ganglion. It conveys general sensitive dendrites, which merely transit the

parasympathetic ganglion and will join its output only, the Nn. ciliares breves.

The Nn. ciliares longi, 2-3, run parallel with the Nn. ciliares breves and penetrate the eyeball

above the optic nerve. They provide the highly sensitive nociceptive innervation of the cornea

(Cornea).

The posterior ethmoidal nerve (N. ethmoidalis post.) is a laterally oriented collateral branch of

the nasociliary nerve. Immediately after its origin it joins the homonymous artery with which

it enters the Foramen ethmoidale post. for innervating the mucosa of the sphenoid and

ethmoid sinuses (Sinus sphenoidalis), (Sinus ethmoidalis).

The anterior ethmoidal nerve (N. ethmoidalis ant.) is the medial endbranch of the nasociliary

nerve. It is is a functionally important branch, innervating meninges, nasal mucosa and skin.

The nerve commences at the anterior ethmoidal foramen, enters it, and passes through its

continuation, a sinuous tunnel connecting the orbit with the anterior cranial fossa (Fossa

cranii ant.) in the company of the homonymous artery. It shows up at the lateral margin of the

Lamina cribrosa, and gives off a thin branch, the anterior meningeal nerve (N. meningeus

ant.) for the innervation of the basal meninges in the anterior cranial fossa. Then the anterior

ethmoidal nerve runs forward along the lateral margin of the Lamina cribrosa till its anterior

end. Here it plunges into the nasal pit (Fossa nasalis) through a slit occurring between the

Crista galli and the Ala cristae galli, named the nasal fissure (fissura nasalis). In the nasal pit

the anterior ethmoidal nerve makes a short run laying in a groove on the concavity of the nasal

bone (Sulcus ethmoidalis, Os nasale). The anterior ethmoidal nerve gives off its endbranches

in the nasal mucosa (Rr. nasales interni) in two sets. The lateral nasal branches (Rr. nasales

latt.) innervate the mucosa of the lateral wall of the nasal pyramid. The medial branches (Rr.

nasales medd.) pass to the nasal septum (Septum nasi) for innervating the septal mucosa. The

other endbranch of the anterior ethmoidal nerve is the R. nasalis externus. This nerve passes

the Foramen nasale and becomes superficial, innervating the skin of the back of the nose

(Dorsum nasi).

The infratrochlear nerve (N. infratrochlearis) is the lateral endbranch of the nasociliary nerve,

continuing its trunk anteriorly along the medial wall of the orbit. It targets the trochlea of the

superior oblique muscle and exits the orbit in below. By its branches completes the

innervation of the conjunctiva of the internal angle of the eye, the Caruncula lacrimalis and

the fundus of the lacrimal sac (Fundus sacci lacrimalis). Its Rr. palpebrales concur at the

innervation of the skin of the eyelids at the internal angle of the eye.

The maxillary nerve (N. maxillaris) (V/2) is the second branch of the trigeminal nerve. It is

the intermediate division; at its origin is purely somatosensitive, formed by sensitive

dendrites, originating in the trigeminal ganglion (nociceptive and tactile) or in the Nc. tractus

mesencephalici nervi trigemini (proprioceptive). The nerve provides sensitive innervation for

the meninges in the middle cranial fossa, for some elements of the orbit, for the mucosa of the

palate and the upper dentoalveolar arch, for the vault of the pharynx (Fornix pharyngis), for

the nasal mucosa and skin of the nose and for the skin of the face. Like in the case of the other

trigeminal branches, vegetative postganglionar axons attach to its distalmost branches.

From its beginning, the nerve runs anteriorly in the middle cranial fossa on the lateral wall of

the cavernous sinus (Sinus cavernosus). Here the nerve emits a collateral branch, after that

leaves the neurocranium through the Foramen rotundum.

Two segments are defined in the extracranial course of the maxillary nerve, according to the

spaces traversed.

The first is the pterygopalatine segment. It is the shorter one and it begins when the nerve

enters the pterygopalatine fossa (Fossa pterygopalatina). This segment is laterally oriented,

stretching just below the ceiling of the bony pit, than the nerve leaves it through the inferior

orbital fissure (Fissura orbitalis inf.). Here the nerve encounters the homonymous artery (A.

maxillaris), the venous Plexus pterygoideus and the buccal fat pad (Corpus adiposum

buccae). Important collateral branches separate here. To this segment the vegetative

pterygopalatine ganglion (Ggl. pterygopalatinum) is morphologically (descriptively) related

(see N. intermedius). There are many links between the nerve and the ganglion, but not all of

them have functional significance.

The second is the infraorbital segment. Reaching the upper surface of the body of the

maxilla (Corpus maxillae), the maxillary nerve moulds into the Sulcus infraorbitalis, and then

enters the Canalis infraorbitalis. Here its name changes into infraorbital nerve (N.

infraorbitalis). This segment ends when the nerve gains on the face traversing the infraorbital

orifice (Foramen infraorbitale) and branches exhaustively. It is to be mentioned that despite

being apparent in the bony orbit (Orbita), remaining under its periosteum (Periorbita), the

nerve is not counted in the orbital region (Regio orbitalis). Collateral branches emerge from

this segment also.

The branches of the maxillary nerve:

R. meningeus medius – is the only intracranial branch of the maxillary nerve. It joins the

frontal branch of the middle meningeal artery (A. meningea med.) for providing the sensitive

innervation of the convexital meninges in the middle and anterior cranial fossae.

The pterygopalatine branches of the maxillary nerve:

Rr. ganglionares – in number of 2, are called by some authors pterygopalatine nerves (Nn.

pterygopalatini). These are equal to what in the systematic anatomy is termed the sensitive

root of the ganglion (Radix sensitiva). They are short branches, suspending the ganglion to the

maxillary nerve and contain sensitive dendrites derived from the maxillary nerve, only to pass

by the ganglion without establishing any connection. These dendrites are transferred

uninterruptedly to sensitive nerves belonging to the system of the maxillary nerve, which, in

this way have their apparent origin in the pterygopalatine ganglion. (see below) The Rr.

ganglionares also convey into the maxillary nerve efferent postganglionar parasympathetic

axons with the real origin in the ganglion. These vegetative efferents are transferred into the

sensitive nerves innervating the cephalic mucosae and into the zygomatic nerve (N.

zygomaticus).

Rr. orbitales, 2-3, are mixed, built up by sensitive dendrites of the maxillary nerve and

sympathetic postganglionar axons deriving from the cervical sympathetic chain. Having their

apparent origin in the pterygopalatine ganglion, they leave it upward, and passing the inferior

orbital fissure, reach the orbit. Here the nerves innervate the orbital periosteum (sensitively)

and provide the vegetative motor innervation of the smooth extrinsic muscle of the eyeball,

the M. orbitalis (of MÜLLER).

The zygomatic nerve (N. zygomaticus) emerges right after the maxillary nerve leaves the

neurocranium. It enters the orbit lateral to the main trunk (the infraorbital nerve), follows its

lateral wall and emits a collateral branch and two endbranches. The nerve is mixed, carries

general somatic afferent dendrites from the maxillary nerve and vegetative postganglionar

parasympathetic axons from the pterygopalatine ganglion. The latter division, as described

previously, is transferred to the lacrimal nerve as a communicating collateral branch (R.

communicans cum nervo zygomatico) (see there). Then, the zygomatic nerve enters a bony

canal of the zygomatic bone which begins with the zygomatico-orbital orifice (Foramen

zygomaticoorbitale). Inside the bone the zygomatic nerve splits in two endbranches. The

medial one is the R. zygomaticofacialis, exits the zygomatic bone through the homonymous

orifice (Foramen zygomaticofaciale) for innervating the skin in the zygomatic region (Regio

zygomatica). The lateral branch is the R. zygomaticotemporalis. This leaves the bone through

its homonymous orifice (Foramen zygomaticotemporale), pierces the temporal muscle (M.

temporalis) and its fascia (Fascia temporalis) and innervates the skin behind the lateral

margin of the orbit.

The posterior superior lateral nasal branches (Rr. nasales postt. supp. latt.) oriented medially,

apparently emerge entirely from the ganglion. But, these thin nerves contain not only sensitive

dendrites of the maxillary nerve, but vegetative postganglionar efferent axons too. Some of

these are parasympathetic with their origin in the pterygopalatine ganglion; others are

sympathetic, ascending from the neck. They leave the pterygopalatine fossa through the

sphenopalatine orifice (Foramen sphenopalatinum) and enter the nasal cavity, accompanied

by the homonymous arteries (Aa. nasales postt. supp.). Here they provide the sensitive

innervation of the mucosa of the upper and middle meatus (Meatus nasi sup., Meatus nasi

medius) and the upper two nasal cornets (Concha nasalis sup., Concha nasalis medius). These

nerves are responsible for the vegetative parasympathetic (and possibly the sympathetic as

well) innervation of the small glands and blood vessels of the lateral nasal mucosa. The

vegetative efferents are much longer than the sensitive branches by whom they enter the nasal

mucosa and thus the vegetative innervation area overlaps with sensitive branches of different

provenance.

The posterior superior medial nasal branches (Rr. nasales postt. supp. medd. seu septales) also

have their apparent origin in the pterygopalatine ganglion. This is again partially true, because

in addition to the postganglionar parasympathetic efferences, the real output of the ganglion,

the nerves contain, like in the previous case, sensitive dendrites and sympathetic

postganglionar axons. The slender nerves pass through the sphenopalatine orifice into the

nasal cavity. Here they continue their medial course in the nasal mucosa of the ceiling of the

nasal pit until reaching the septum, then descend anteriorly in the septal mucosa. These nerves

all participate in the sensitive and vegetative innervation of the mucosa of the nasal septum,

but one of the branches, the stronger nasopalatine nerve (N. nasopalatinus) has a longer

course. Together with the homonymous artery it targets the incisive foramen (Foramen

incisivum), passes it and ends up beneath the oral mucosa of the hard palate (Palatum durum).

The nasopalatine nerve, with its anterior and laterally turning branches innervates the gum till

the canine tooth. Some of its branches run posterior to intermingle with the branches of the N.

palatinus longus and innervate the remaining palatine mucosa.

The pharyngeal branch (N. pharyngeus) is a minor twig that detaches from the ganglion in the

posterior. It joins the homonymous artery and exits the pterygopalatine fossa on postero-

medial by traversing the palatinovaginal canal (Canalis palatinovaginalis). It is to be found on

the external skull base. The nerve provides a sensitive and possibly vegetative innervation for

the mucosa of the pharyngeal vault (Fornix pharyngis).

The greater palatine nerve (N. palatinus major) separates downwards from the pterygopalatine

ganglion and maintains its direction by entering the homonymous canal (Canalis palatinus

maj.), along other nerves and arteries. By exiting the canal through the Foramen palatinum

maj. it reaches the hard palate and splits in branches. The branches turn anteriorly on the

palate to intricate with similar branches from the nasopalatine nerve, with whom they should

not be confused. This nerve, likewise, carries sensitive dendrites and vegetative

postganglionar axons to the palatine mucosa.

The lesser palatine nerves (Nn. palatini minores) have a similar origin and functional

significance as the previous. They share the same exit way from the pterygopalatine fossa, but

traverse the Foramen palatinum minor. Ended up on the palate, these branches course

posteriorly to provide sensitive and vegetative innervation for the soft palate (Palatum molle,

Velum palatinum).

The posterior inferior lateral nasal branches (Rr. nasales postt. inff. latt.) segregate either from

the ganglion, either from the above mentioned palatine branches. They exit the palatine canal

anteriorly through minute, un-named orifices and reach the nasal pit. There they innervate the

mucosa of the lower meatus (Meatus nasi inf.), the lower nasal cornet (Concha nasalis inf.)

and the mucoperiosteum of the maxillary sinus (Sinus maxillaris). Their functional and

systematic provenance and significance is identical to the other nasal nerves.

The superior alveolar nerves (Nn. alveolares supp.) emerge from the trunk of the maxillary

nerve in three sets. All of them penetrate into the body of the maxilla and by branching and

recombination of the resulting branches form an extensive nervous plexus, the Plexus dentalis

sup. at the border between the body of the maxilla (Corpus maxillae) and its alveolar process

(Processus alveolaris sup.). This plexus contains somatosensitive dendrites of all functional

types. From the plexus delicate sensitive branches are sent into the alveoli of the teeth. Here

they segregate for the sensitive innervation of the teeth and the surrounding periodontium as

the superior dental branches (Rr. dentales supp.) and for the upper gum (Rr. gingivales supp.).

The Rr. alveolares supp. postt. in number of 2-3, are dispatched in the pterygopalatine fossa.

After their origin, they descend and leave the pterygopalatine fossa laterally, through the

sphenomaxillary fissure (Fissura pterygomaxillaris), together with the homonymous arteries.

The nerves then travel on the tuber of the maxilla (Tuber maxillae) until reaching their proper

orifices (Foramina alveolaria) for penetrating into the Corpus maxillae. By means of the

superior dental plexus they innervate the molar teeth, their periodontium and the neighboring

gum.

The following branches of the infraorbital part of the maxillary nerve actually originate from

the part bearing the name of N. infraorbitalis:

The R. alveolaris sup. medius proceeds downward fitting into a narrow canal of the lateral

wall of the maxillary sinus. It is the nerve of the premolar teeth and the corresponding

periodontium and gum. It might be absent.

The Rr. alveolares supp. antt. are constant branches. Like the previous branch, they remain

concealed in the Corpus maxillae. Their origin is close to the infraorbital orifice. They

descend in the anterior wall of the maxillary sinus, in their own bony canal, the canalis

sinuosus. These provide the innervation of the incisor teeth and their entourage. A twig of this

nerve reaches the nasal cavity and innervates the mucosa on the anterior part of its floor.

The infraorbital nerve (N. infraorbitalis) is the direct continuation of the maxillary nerve, but

it can be conceived as its endbranch. Exits the Corpus maxillae through the infraorbital orifice

and immediately splits off in its endbranches. On the face the nerve can be discovered

between the layers of the tegument, in a narrow space defined medially by the M. levator labii

superioris and laterally by the M. levator anguli oris. The branches released are all

somatosensitive:

The Rr. palpebrales inff. ascend to the lower eyelid, omit the M. orbicularis oculi for the

innervation of the skin and the conjunctiva.

The Rr. nasales externi innervate the skin of the Ala nasi.

The Rr. nasales interni enter the nasal pyramid at its base and innervate the skin lining the

nasal vestibule (Vestibulum nasi).

The Rr. labiales supp. descend on the bony surface of the Fossa canina and innervate the

covering skin and the mucosal lining of the upper lip (Labium sup.).

The mandibular nerve (N. mandibularis) (V/3) is the thickest, lateral branch of the

trigeminus. The trunk of the nerve is short, of only 2 cm. It takes its origin from the lateral

part of the convexity of the trigeminal ganglion, turns downward and exits the middle cranial

fossa through the Foramen ovale, reaching the infratemporal fossa (Fossa infratemporalis).

Here the mandibular nerve is placed antero-medial to the upper head of the lateral pterygoid

muscle and branches exhaustively. A vegetative parasympathetic ganglion, the Ggl. oticum is

attached to the nerve. (see at the glossopharyngeal nerve) The motor root of the trigeminal

nerve (Portio minor), passing beneath the trigeminal ganglion entirely joins the exiting

sensitive division of the nerve. This is a mixed nerve, because it is formed by peripheral

sensitive dendrites originating in the ganglion and the motor axons emerging from the pontine

motor nucleus.

It provides general sensitive afferent innervation for the meninges in the middle cranial fossa,

the outer auditory meatus (Meatus acusticus ext.), the inferior part of the mouth (including the

lower dentoalveolar arch, the tongue, the Diaphragma oris), the lateral wall of the mouth, the

skin of the chin and of the cheek up to the angle of the mandible (Angulus mandibulae), the

Isthmus faucium and the skin of the temple.

The mandibular nerve conveys sensitive proprioceptive dendrites for the masticator muscles,

whom it provides motor innervation too, and for the ATM. The nerve also transmits

proprioceptive dendrites for the facial and lingual muscles, but these fibers, at the periphery of

the nervous tree, are taken over by the nerves supplying the motor innervation for these

muscles.

The mandibular nerve, by its branch, the lingual nerve, serves as a guidewire the special

sensorial fibers into the lingual mucosa, along the trigeminal fibers for general sensitivity.

These sensorial fibers are peripheral dendrites belonging to the system of the intermediate

nerve, originating in its sensory ganglion, the Ggl. geniculi.

Similar to the other trigeminal branches, vegetative postganglionar axons attach to the

mandibular nerve’s distalmost branches.

The branches of the mandibular nerve are broadcasted only extracranially, where the nerve

branches in the form of a broom. Several branches (buccal, pterygoid, temporal and

masseteric nerves) usually have a common origin by means of a short primary trunk, the

antero-superior primary division of the mandibular nerve. Instead, the lingual, inferior

alveolar and auriculotemporal nerves emerge individually, and so do some smaller branches

also. Listed in a systematic anatomical approach, the branches of the mandibular nerve are:

The R. meningeus (or N. spinosus) is a collateral sensitive branch emerging in the

infratemporal region, just beneath the Foramen ovale. The nerve turns laterally, than re-enters

the middle cranial fossa through the Foramen spinosum, joins the middle meningeal artery

and completes the innervation of the convexital meninges of the middle cranial fossa by

splitting in two branches. These follow the temporal and, respectively, the parietal branch of

the artery.

There are two short, un-nominated branches sent to the otic ganglion. Containing sensitive

dendrites from the trigeminal ganglion, these nervelets serve as apparent, sensitive roots for

the ganglion. Naturally, these somatosensitive fibers are only tangent to the parasympathetic

otic ganglion and are incorporated in sensitive branches of the trigeminal system. On the

analogy to other similar ganglia, they could be named Rr. ganglionares.

The medial pterygoid nerve (N. pterygoideus med.) separates from the anterior primary trunk

of the mandibular nerve. This nerve contains somatomotor axons for the motor innervation of

the homonymous muscle (M. pterygoideus med.). The nerve also brings proprioceptive

sensitive dendrites for this muscle. Soon an after its origin, the medial pterygoid nerve gives

off two slender branches. These are the N. tensoris veli palatini and the N. tensoris tympani,

similarly somatomotor nerves, each for the homonymous muscle. The muscles are to be found

in the infratemporal region. These small nerves might apparently emerge from the otic

ganglion as its false branches.

The lateral pterygoid nerve (N. pterygoideus lat.), like the previous one, is a somatomotor

branch of the primary common trunk. It innervates the homonymous muscle (M. pterygoideus

lat.) with motor and proprioceptive innervation by penetrating the intermuscular space in

between the two heads of the muscle.

The Nn. temporales proff. (2-3) are given off in a lateral direction from the primary trunk of

the mandibular nerve. From the Foramen ovale they stretch laterally just beneath the outer

skull base, above the upper head of the lateral pterygoid muscle. Reaching the Crista

infratemporalis the nerves turn upwards into the temporal fossa (Fossa temporalis) on the

medial, profound surface of the temporal muscle (M. temporalis) and supply it with motor and

proprioceptive innervation.

The masseteric nerve (N. massetericus) is the next branch of the primary trunk. It has a lateral

direction between the outer skull base and the upper head of the lateral pterygoid muscle. It

emits 4 minute branches for the ATM, then leaves the infratemporal region by crossing from

behind the coronoid process (Processus coronoideus) and passing above the Incisura

mandibulae. The nerve transmits somatomotor axons for the masseter muscle (M.

massetericus), proprioceptive dendrites for the same muscle and for the ATM and its

surroundings.

The buccal nerve (N. buccalis) is the only sensitive branch of the anterior primary trunk of the

mandibular nerve. It has a relatively long course: descends at first, than sloping anteriorly it

passes the intermuscular slit between the upper and lower heads of the lateral pterygoid

muscle for entering the pterygomandibular space (Spatium pterygomandibulare). It is the

anteriormost formation of this space, then leaves and branches exhaustively on the lateral

surface of the buccinator muscle (M. buccinator). Some of these endbranches turn laterally

and innervate the skin of the cheek (Bucca), while others penetrate the muscle to innervate the

mucosa of the oral vestibule (Vestibulum oris) up to the Fornix vestibuli sup. and inf.

In addition to the sensitive dendrites for innervating the skin and the mucosa of the cheek, the

nerve also transports postganglionar parasympathetic and sympathetic axons for the

vegetative innervation of the small salivary glands of the buccal mucosa. The parasympathetic

postganglionar axons stem in the otic ganglion, whereas the sympathetic come from the

sympathetic plexus surrounding the external carotid artery (A. carotis ext.) by means of the

spurious sympathetic root of the otic ganglion.

The lingual nerve (N. lingualis) is a strong branch of the mandibular nerve. Three parts of it

are encountered, according to the spaces transited. The origin of the nerve is in the

infratemporal region, right underneath the Foramen ovale. Then the descending nerve enters

the space between the two pterygoid muscles, where its first segment lies. Here the lingual

nerve parallels the inferior alveolar nerve and the maxillary artery (A. maxillaris) and

incorporates an other nerve, the N. chorda tympani. This belongs to the system of the

intermediate nerve, carries specific sensorial dendrites originating in the geniculate ganglion

(Ggl. geniculi) and preganglionar parasympathetic axons stemming in the superior salivatory

nucleus (Nc. salivatorius sup.) of the pons. The slender Chorda tympani approaches the

lingual nerve from behind and below. Then the lingual nerve continues with its second

segment in the pterygomandibular space, between the medial pterygoid muscle and the medial

side of the upper part of the Ramus mandibulae. Here the lingual nerve courses together with

the inferior alveolar vessels and nerve and has an antero-inferior direction. The lingual nerve

leaves the pterygomandibular space, and by that the infratemporal region, just above the

posterior end of the Linea mylohyoidea by piercing the superior constrictor muscle of the

pharynx (M. constrictor pharyngis sup.), between its pterygopharyngeal and mylopharyngeal

parts (Pars pterygopharyngea, Pars mylopharyngea). Transiting the pharyngeal wall, the

lingual nerve commences its third, submandibular part. In the submandibular region at first it

is placed on the lateral side of the hyoglossus muscle (M. hyoglossus), then passes through the

upper part of the narrow slit between the hyoglossus and mylohyoideus muscles. Here the

nerve stretches in the company of the sublingual artery and vein (A., V. sublingualis), the

submandibular duct (Ductus submandibularis) and lymphatic vessels, well beyond the

hypoglossal nerve. The nerve then leaves the intermuscular space and continues with its

fourth and final sublingual part. This portion is placed in the Sulcus lat. linguae, a furrow

between the mylohyoid and the geniohyoid (M. geniohyoideus) muscles, where the nerve

becomes superficial, covered by the sublingual mucosa only.

Functionally, the lingual nerve is mixed. Descriptively, this stays for its more peripheral part

and its branches. It is general sensitive due to the dendrites emerging from the trigeminal

ganglion, specific sensorial for the sense of taste by the dendrites from the Chorda tympani

and vegetative parasympathetic preganglionar by the axons arriving by the means of the same

junction. The terminal branches of the lingual nerve contain postganglionar efferent axons

stemming in the submandibular ganglion (Ggl. submandibulare). The proprioceptive

dendrites travelling initially in the lingual nerve are transferred to the hypoglossal nerve.

The lingual nerve begins to emit branches from its third segment. The Rr. isthmi faucium are

sent off for the general sensitive innervation of the lateral wall of the throat (Isthmus faucium),

the compartment of the palatine tonsil (Tonsilla palatina) and the posterior part of the

Diaphragma oris.

The R. communicans cum nervo hypoglosso only contains the proprioceptive fibres exchanged

between the lingual and hypoglossal nerves.

The Rr. ganglionares are small twigs connecting the lingual nerve to the submandibular

ganglion. These tiny nerves are composed by the preganglionar parasympathetic axons which

joined the lingual nerve just previously via the N. chorda tympani, and represent the real,

parasympathetic root of the ganglion. It is important to realize, that a number of

postganglionar axons turn back into the lingual nerve approaching their targets together with

the sensitive dendrites. These are not specially designated branches, thus the Rr. ganglionares

from the point of view of the systematic anatomy are bi-directional, carrying preganglionar

axons from the lingual nerve to the ganglion and postganglionar axons from the ganglion to

the nerve. It is assumed that the posterior group of the ganglionar branches contain

preganglionar axons and the anterior set of the ganglionar branches convey postganglionar

fibres.

The lingual branches (Rr. linguales) penetrate the tongue and provide the nociceptive thermal,

tactile and specific sensorial innervation to the lingual mucosa. The vegetative innervation for

the lingual small glands is broadcasted by means of these branches also.

The sublingual nerve (N. sublingualis) continues the main trunk of the lingual nerve. It

courses anterior in the Sulcus lat. linguae and spreads off in branches providing sensitive

innervation for the sublingual mucosa, the gum of the inner slope of the inferior alveolar arch

(Arcus alveolaris) and vegetative postganglionar innervation for the submandibular and

sublingual salivary glands (Gl. submandibularis, Gl. sublingualis). Systematically these are

termed glandular branches (Rr. glandulares), but descriptively, they can emerge from the

lingual nerve or from the sublingual nerve or directly from the ganglion.

The inferior alveolar nerve (N. alveolaris inf.) is the thickest branch of the mandibular nerve.

It starts in the infratemporal region and passes anteriorly under the lateral pterygoid muscle.

Three segments are to be defined according to its anatomical environment. With its

interpterygoid segment the nerve lies between the two pterygoid muscles, lateral to the lingual

nerve, in the vicinity of the maxillary artery (A. maxillaris). The second, pterygomandibular

segment begins where stretching downwards, the inferior alveolar nerve passes between the

medial and lateral pterygoid muscles on its way to the Foramen mandibulae. In this space it is

shadowed from medial by the lingual nerve and the inferior alveolar artery (A. alveolaris inf.).

The third segment is the mandibular one, where the nerve courses in the mandibular canal

(Canalis mandibulae).

Functionally, the nerve is mixed by conveying dendrites for the general sensation and

somatomotor by its component of efferent axons. Likely, the nerve also conveys vegetative

postganglionar axons for the small salivary glands of the inferior labial mucosa.

The inferior alveolar nerve sends off branches beginning with its pterygomandibular segment.

The mylohyoid nerve (N. mylohyoideus) is the first collateral branch. It separates from the

nerve in the pterygomandibular space, surrounds from posterior and inferior the insertion of

the sphenomandibular ligament (Lig. sphenomandibulare) on the Lingula mandibulae. In the

case of a bifid ligament, the nerve escapes between the two inserting fascicles. Than the nerve

goes behind the posterior edge of the mylohyoid muscle and stretches further on its inferior

surface, on the medial side of the body of the mandible (Corpus mandibulae), in the Sulcus

mylohyoideus. It provides a branch for the anterior belly of the digastricus muscle (M.

digastricus, Venter anterior). In addition to the motor innervation, the mylohyoid nerve

probably provides proprioceptive innervation for these muscles.

All its way, in the mandibular canal, from the nerve split up branches which by recombination

elaborate a nervous plexus, the Plexus dentalis inf. This is situated inside the bony matter,

beyond the mandibular canal, between the body of the mandible (Corpus mandibulae) and its

alveolar process (Processus alveolaris inf.). From the plexus fine sensitive nervelets are

dispatched into the alveoli of the teeth. Here they break up in further branches and sensitively

innervate the teeth, the neighboring gum and the periodontium (Rr. dentales inff.), (Rr.

gingivales inff.). Like its superior homologue, this inferior dental plexus contains

somatosensitive dendrites of all functional types.

The main trunk of the inferior alveolar nerve bifurcates in two terminal branches, which for a

while run paralelly together in the bony canal. The lower one, the mental nerve (N. mentalis)

leaves the mandibular canal through the Foramen mentale and innervates the skin of the chin

with the Rr. mentales, the mucosa of the lower lip (Labium inf.) by the Rr. labiales and the

adjacent gum with the Rr. gingivales. The counterpart of the mental nerve, the incisive nerve

(n. incisivus) continues the way of the inferior alveolar nerve and by similar branching pattern

takes part in the inferior dental plexus. It concurs in the innervation of the canine and the

incisor teeth.

The lateralmost endbranch of the mandibular nerve is the auriculotemporal nerve (N.

auriculotemporalis). The nerve stems by two equal roots which surround the middle

meningeal artery and then unite latero-posterior to it. After its trunk is formed, the

auriculotemporal nerve courses backwards on the lateral surface of the lateral pterygoid

muscle, above the maxillary artery. Than the nerve escapes through the slit formed between

the neck of the mandible (Collum mandibulae) and the sphenomandibular ligament and enters

the parotid region (Regio parotidea). Here turns superficial just anterior the tragus (Tragus)

and becomes the posterior element of the superficial temporal vasculo-nervous bundle. The

nerve is purely sensitive at its origin but soon acquires vegetative postganglionar branches

from the otic ganglion, becoming in this way mixed, general sensitive and parasympathetic.

After its full development, the nerve begins to emit branches.

The N. meatus acustici externi penetrates between the bony and the cartilaginous parts into the

external auditory meatus (Meatus acusticus ext.), innervating its skin and the periosteum. A

branch of this, the R. membranae tympani innervates the outer (lateral), cutaneus surface of

the tympanic membrane.

The Rr. parotidei convey vegetative postganglionar parasympathetic axons with their origin in

the otic ganglion and others stemming in the cervical sympathetic, to the parotid gland

(Glandula parotidea).

The R. communicans cum nervo faciali is a route for the proprioceptive dendrites for

switching from the trigeminal system into the system of the facial nerve, for collecting the

proprioceptive information from the facial muscles.

The anterior auricular nerves (Nn. auriculares antt.) innervate the tragus and the surrounding

skin.

The superficial temporal nerves (Nn. temporales superff.) climb in the hypoderm into the

temporal region (Regio temporalis), where they follow the branches of the superficial

temporal artery (A. temp. superf.) and innervate the skin of the temple.

The N. VI. or the abducent nerve (N. abducens)

The abducent nerve is a somitic somatomotor efferent encephalic nerve with the appearance

of a slender bundle.

It only innervates the lateral rectus muscle of the eye (M. rectus lat. bulbi).

The proper origin lies in the pons, in the abducent nucleus (Nc. nervi abducentis).

The apparent origin is to be found in the sulcus bulbopontinus, just above the bulbar

pyramids (Pyramis bulbi).

The course of the intracranial segment of the nerve is the longest of all the encephalic nerves.

It advances in the pontine cistern (Cisterna pontis) just above the superior anterior cerebellar

artery (A. cerebellaris ant. sup.) and reaching the clivus ascends on its surface. The nerve then

pierces the dura mater a little below and medial to the exit point of the trigeminal nerve. It

penetrates the cavernous sinus and continues its anterior course within its lateral wall by

crossing from lateral the internal carotid artery and from medial the ophtalmic nerve. The

nerve leaves the cavernous sinus at its anterior side and after a very short run in the middle

cranial fossa enters the orbit through the superior orbital fissure. Here the abducent nerve

traverses the common tendinous ring of the extrinsic ocular muscles and reaches its target, the

medial side of the lateral rectus muscle (M. rectus bulbi lat.).

The abducent nerve has no branches.

The N. VII. or the facial nerve (N. facialis)

The facial nerve is a somitic somatomotor efferent encephalic nerve. Sometimes it is listed as

the intermediofacial nerve (N. intermediofacialis) and it is attributed other function also. In

fact, in the descriptive anatomy the facial nerve is distinct to the intermediate nerve (N.

intermedius) and they segregate functionally too.

The facial nerve innervates the muscles of the facial expression and several other muscles of

the head and neck as well, as follows:

the mentalis muscle (M. mentalis),

the depressor of the lower lip muscle (M. depressor labii inf.-is),

the depressor of the corner of the mouth muscle (M. depressor anguli oris),

the orbicularis oris muscle (M. orbicularis oris),

the elevator of the upper lip muscle (M. levator labii sup.-is),

the elevator of the upper lip and of the ala nasi muscle (M. levator labii sup.-is aleque nasi),

the elevator of the corner of the mouth muscle (M. levator anguli oris),

the buccinator muscle (M. buccinator),

the risorius muscle (M. risorius),

the greater zygomatic muscle (M. zygomaticus maj.),

the lesser zygomatic muscle (M. zygomaticus min.),

the nasalis muscle (M. nasalis),

the procerus muscle (M. procerus),

the corrugator of the eyebrow muscle (M. corrugator supercilii),

the depressor of the eyebrow muscle (M. depressor supercilii),

the orbicularis of the eye muscle (M. orbicularis oculi),

the occipitofrontal muscle (M. occipitofrontalis),

the muscles of the external ear (M. auricularis ant., sup., post.),

the platysma muscle (M. platysma),

the stylohyoid muscle (M. stylohyoideus),

the posterior belly of the digastric muscle (M. digastricus, Venter post.) and

the stapedius muscle (M. stapedius).

The proper origin lies in the pons, in the facial nucleus (Nc. nervi facialis), the somitic

somatomotor nucleus, wherefrom the efferent axons emerge.

The apparent origin is to be found ventrally on the brain stem, in the sulcus bulbopontinus,

above the bulbar olives (Oliva bulbaris), below the middle cerebellar peduncle (Pedunculus

cerebellaris medius), in the cerebellopontine angle, antero-medial to the flocculus of the

cerebellum (Flocculus). Its emergence lies laterally to the origin of the abducent nerve, medial

to the vestibulocochlear nerve. The intermediate nerve has its origin just lateral to the facial

nerve, so close, that the two nerves apparently merge.

The course of the nerve is divided in three segments, according to its relationships to the

skull base and the petrous part of the temporal bone (Pars petrosa ossis temporalis):

intracranial, intrapetrous and extrapetrous.

The first, intracranial segment of the facial nerve begins at its apparent origin and keeps until

the nerve penetrates into the temporal bone. From its apparent origin, the nerve has a proper

pial envelope but is ensheathed by the arachnoidea together with the intermediate and the

vestibulocochlear nerves. The nerves are joined by the labyrinthic artery (A. labyrinthica) and

they run together upwards and mostly laterally for entering the internal auditory porus (Porus

acusticus int.), then its continuation, the internal auditory meatus (Meatus acusticus int.). Here

the facial nerve is situated anterior and superior and heads the facial area (Area nervi facialis)

of the fundus of the meatus (Fundus meatus acustici int.). It is to be mentioned, that the short

run in the internal auditory meatus is clinically significantly different, called intracanalar

segment.

The second, intrapetrous segment of the facial nerve commences where in the facial area the

nerve perforates the dura mater and enters its bony canal, the Canalis facialis (of FALLOPE).

Here the facial nerve is accompanied by the intermediate nerve and meets the ascending

stylomastoid artery (A. stylomastoidea). The facial canal is of circa 34 mm in length, being

divided in three parts according to the structures it passes by, delineated by two curvatures.

The first, proximal part of the canal is called labyrinthic, lies perpendicular to the longitudinal

axis of the petrous part of the temporal bone, namely antero-lateral and has a 4 mm length. In

the vicinity of the anterior side of the petrous bone, the canal makes a sharp posterior turn.

The nerve inside forms the knee (Geniculum nervi facialis) and at this level begins the second

part of the facial canal. This is the tympanic part of 12 mm in length, running laterally in the

vicinity of the tympanic cavity (Cavum tympani), where its ceiling (the Tegmen tympani)

meets the medial (labyrinthic) wall. The canal visibly bulges into the tympanic cavity, where

it could be identified as the Prominentia canalis facialis above the Promontorium and the oval

window (Fenestra vestibuli). Then, after a widely arching inferior turn the third portion of the

canal, called the mastoid part begins. This second turn lies above the Aditus ad antrum, and

sometimes is called the inferior knee of the facial canal. The mastoid part is of 18 mm,

descends vertically and ends inferiorly with its exit orifice, the Foramen stylomastoideum.

Here the bony canal’s wall is still formed by condensed bone but it is surrounded by the

pneumatized massive of the mastoid labyrinth. It is to be mentioned, that the facial canal has 4

additional exit openings where nervelets escape out from the temporal bone.

The third, extrapetrous segment of the facial nerve is extracranial also. It begins where the

nerve leaves through the stylomastoid foramen and is joined by the stylomastoid artery. The

nerve courses infero-lateral and enters the compartment of the parotid gland (Glandula

parotis) and breaks up into its endbranches. The glandular tissue moulds on the nerve and its

branches and it is not actually penetrated by the nerves.

Branches of the facial nerve are emitted from the intrapetrous part as collateral branches, and

the nerve, at the end of its extrapetrous segment bifurcates into two endbranches. In turn,

these two endbranches ramify again but the resulting nerves rejoin each other just to give birth

to tertiary branches. This nervous arbor is situated mainly in one single sagittal plane,

embedded in the parotid gland as the intraparotid plexus (Plexus intraparotideus). From the

trunk or from this plexus emerge the actual definitive branches of the facial nerve, as follows:

The stapedius nerve (N. stapedius) is a minute branch intended to the M. stapedius. It

emerges still in the intrapetrous segment, leaves the facial canal through its own orifice for

meeting the muscle whom it supplies with axons for the motor innervation.

The posterior auricular nerve (N. auricularis post.) exits the facial canal in its mastoid part

through another small lateral opening. Escaping from the bone just anterior to the mastoid

process, the nerve ascends behind the external ear. It gives birth to several muscular branches:

The R. occipitalis ascends to the occipital belly of the occipitofrontal muscle (M.

occipitofrontalis, Venter occipitalis).

The R. auricularis turns anterior and enters the external ear for innervating the auricular

muscles.

The R. digastricus is directed inferior for the posterior belly of the digastric muscle (M.

digastricus, Venter post.).

The R. stylohyoideus courses medially for the stylohyoid muscle. It might emerge from a

common trunk with the previous branch.

The R. communicans cum nervo glossopharyngeo stems from the inferior ganglion (Ggl. inf.)

of this nerve.

The temporofacial nerve and the cervicofacial nerve are the actual endbranches of

the facial nerve, arising below the stylomastoid orifice. They soon split up in further branches

which by repeated recombination form the intraparotid plexus. From this plexus originate the

branches of higher order exiting the gland and turning superficial on the side of the Ramus

mandibulae spread in a fan-like shape.

The Rr. temporales climb superficially in the skin of the masseteric region, then crossing the

zygomatic arch (Arcus zygomaticus) innervate the anterior muscle of the auricle, the frontal

belly of the occipitofrontal muscle (M. occipitofrontalis, Venter frontalis), the upper part of

the M. orbicularis oculi, the depressor of the eyebrow muscle (M. depressor supercilii) and

the M. corrugator supercilii.

The Rr. zygomatici course anterior and innervate the zygomatic muscles (M. zygomaticus

maj., M. zygomaticus min.) and the lower part of the M. orbicularis oculi.

The Rr. buccales are the motor nerves of the upper perioral and periorofacial muscles. They

are directed forward and spread for the orbicularis oris muscle (M. orbicularis oris), the

nasalis muscle (M. nasalis), the procerus muscle (M. procerus), the elevator of the upper lip

muscle (M. levator labii sup.-is), the elevator of the upper lip and of the ala nasi muscle (M.

levator labii sup.-is aleque nasi), the elevator of the corner of the mouth muscle (M. levator

anguli oris) and the buccinator muscle (M. buccinator).

The R. marginalis mandibulae parallels from above the basis of the mandible (Basis

mandibulae). It emits branches which innervate the lower perioral muscles, namely the

mentalis muscle (M. mentalis), the depressor of the lower lip muscle (M. depressor labii inf.-

is), the depressor of the corner of the mouth muscle (M. depressor anguli oris) and the risorius

muscle (M. risorius).

The R. colli (or R. cervicalis) descends from the corner of the mandible superficial to the

platysma muscle (Platysma) whom it innervates. This nerve has a communicating branch with

the cervical plexus (Plexus cervicalis) via the superior branch of the transverse cervical nerve

(R. sup., N. transversus colli), called the ansa cervicalis superficialis.

The N. VII’. or the intermediate nerve (N. intermedius)

The intermediate nerve (of WRISBERG) is a general sensitive afferent, specific sensorial

afferent and a vegetative parasympathetic efferent encephalic nerve with the appearance of a

slender bundle, attached to the facial nerve, with whom descriptively forms the

intermediofacial nerve.

It sensitively innervates the inferior part of the external auditory meatus, provides sensorial

innervation for collecting the taste information from the anterior 2/3 of the dorsum of the

tongue and secretor parasympathetic innervation of the submandibular, sublingual and

lacrimal glands, as well for the small glands of the oral and nasal mucosae.

The proper origin lies in the pons, in the superior salivary nucleus (Nc. salivatorius sup.) and

in the medulla, in the nucleus of the solitary tract (Nc. tractus solitarii). At its origin, the

intermediate nerve consists of efferent vegetative preganglionar axons and afferent sensorial

and sensitive axons.

The apparent origin is in the sulcus bulbopontinus, above the bulbar olives (Oliva bulbaris),

below the middle cerebellar peduncle (Pedunculus cerebellaris medius), in the

cerebellopontine angle, antero-medial to the flocculus of the cerebellum (Flocculus). Its

emergence lies medial to the vestibulocochlear nerve, just lateral to the facial nerve, so close,

that the two nerves apparently merge.

The course of the intermediate nerve is divided into an intracranial and an intrapetrous

segment. By its intracranial segment the intermediate nerve has an intimate syntopy with the

facial and vestibulocochlear nerves with whom traces upward and lateral, in a common

arachnoid sheath. This nervous bunch is joined by the labyrinthic artery, with whom together

enter the internal auditory porus and meatus. Here is the nerve’s clinically defined intracanalar

segment.

The petrous segment commences at the bottom of the meatus, where the vestibulocochlear

nerve and the labyrinthic artery detach from the intermediofacial. Here the intermediate nerve

shares the same Canalis facialis with the facial nerve. At the knee of the facial canal the

intermediate nerve meets its sensitive and sensorial ganglion, the geniculate ganglion (Ggl.

geniculi seu Ggl. geniculatum). The ganglion contains the perikarya of the sensitive and

sensorial neurons and is bypassed by the preganglionar axons. The peripheral processes

(dendrites) of the ganglionar cells travel further in the branches of the intermediate nerve.

Branches: the nerve gives rise to no collaterals, instead, after leaving the geniculate ganglion,

it splits into two endbranches within the facial canal. These leave the facial canal through

small, proper orifices and travel on some extent inside the petrous part of the temporal bone.

In addition to its own branches, the intermediate nerve exchanges fibers with other encephalic

nerves. The branches are as follows:

The greater petrosal nerve (N. petrosus maj.) originates right after the geniculate ganglion.

It is built up by vegetative parasympathetic preganglionar axons. The nerve is engaged in its

own canal (Canalis nervi petrosi majoris) and penetrates through its homonymous orifice

(Hiatus canalis nervi petrosi majoris) into the middle cranial fossa. Here it courses postero-

medially on the anterior side of the petrous part of the temporal bone (Facies ant. partis

petrosae) in the homonymous groove (Sulcus nervi petrosi majoris), covered by the dura

mater (Dura mater encephali) towards the Foramen lacerum. Leaves the middle cranial fossa

through this orifice and shows up in the infratemporal region. Here the greater petrosal nerve

is joined by the deep petrosal nerve (N. petrosus prof.) and together form the nerve of the

pterygoid canal (N. canalis pterygoidei) (the Vidian nerve). This nerve, as its name suggests,

enters the pterygoid canal (Canalis pterygoideus), where it meets the homonymous artery (A.

canalis pterygoidei). The nerve exits into the pterygopalatine fossa and enters the

pterygopalatine ganglion (Ggl. pterygopalatinum), for whom it serves as the parasympathetic

root.

The pterygopalatine ganglion (Ggl. pterygopalatinum) is a small peripheral nervous

structure situated in the upper part of the pterygopalatine fossa, infero-medial to the maxillary

nerve. In the ganglion reside ganglionar („postganglionar”) neurons of the vegetative

parasympathetic division of the intermediate nerve. It is morphologically bound by the means

of its branches to the intermediate, the trigeminal and the sympathetic nervous trees, but

functionally and systematically belongs to the system of the intermediate nerve only.

Systematically, it has three roots and one set of branches. Out of the three roots one is real,

with functional value, the other two are spurious.

The parasympathetic root (Radix parasympathetica) is the only proper root of the ganglion,

conveying the preganglionar axons, originating in the superior salivary nucleus. As shown, at

the beginning these fibers travel with the intermediate nerve, then they separate from it by the

greater petrosal nerve (N. petrosus maj.), by whom finally reach the ganglion. Here the

preganglionar axons synapse on the ganglionar cells, which in turn give rise to the

postganglionar axons, the output of the pterygopalatine ganglion.

The sympathetic root (Radix sympathetica), a generic feature of the parasympathetic

ganglions, only apparently belongs to the pterygopalatine ganglion, as these axons merely

transit it. Their origin is in the superior cervical ganglion (Ggl. cervicale sup.) of the cervical

sympathetic chain, then pass into the nervous plexus surrounding the internal carotid artery

(Plexus caroticus internus). From the latter, in the infratemporal fossa, a distinct structure, the

deep petrosal nerve (N. petrosus prof.) will separate and lead the postganglionar sympathetic

axons into the N. canalis pterygoidei. In the pterygopalatine fossa these fibers pass the

pterygopalatine ganglion without making any functional connection with it and join the

vegetative branches emerging from here. By the means of them, the sympathetic axons join

the Rr. orbitales and innervate the M. orbitalis (of MÜLLER). Obviously, these branches do

not belong to the functional output of the ganglion.

The sensitive root (Radix sensitiva) is represented by two trigeminal branches, the Rr.

ganglionares of the infraorbital nerve. The minute nerves, descriptively termed Nn.

pterygopalatini contain sensitive dendrites originating in the trigeminal ganglion, and they

pass through the pterygopalatine ganglion without being functionally linked to it. It is to be

mentioned, that these pterygopalatine nerves have a mixed composition and are not only

spurious roots of the pterygopalatine ganglion but its real exit ways also, as they, along the

incoming sensitive dendrites, carry out postganglionar axons originating here.

The functional output of the pterygopalatine ganglion is conveyed by some trigeminal

branches of the maxillary nerve, which passing near or through the ganglion take up the

postganglionar axons. These are the above mentioned Rr. ganglionares or pterygopalatine

nerves, the nerves innervating the nasal mucosa, the pharyngeal branch and the palatine

nerves, as listed at the maxillary nerve (see there). All these nerves contain the postganglionar

parasympathetic axons originating in the ciliary ganglion, other postganglionar sympathetic

axons just transiting it and general somatic sensitive dendrites from the trigeminal system.

One set of postganglionar axons, as seen, pass into the system of the maxillary nerve (the

zygomatic nerve) and from there to the system of the ophtalmic nerve and innervate the

lacrimal gland. Others remain in the maxillary twigs and supply the small glands of the nasal

and palatine mucosae and the vault of the pharynx.

The R. communicans cum plexo tympanico is a weak branch going in its own bony canal

into the tympanic cavity to the tympanic plexus (Plexus tympanicus). It represents a

connection to the otic ganglion (Ggl. oticum).

The R. communicans cum nervo vago is another small branch emitted for the vagus nerve at

the inferior part of the facial canal.

The chorda tympani nerve (N. chorda tympani) can be considered the endbranch of the

intermediate nerve. It leaves the facial canal just above the stylomastoid orifice and

immediately enters in its own bony canal, the Canaliculus chordae tympani. This has an

almost inverse course than the facial canal, ascends and turns anteriorly to open into the

tympanic cavity. The opening is a small orifice (Apertura tympanica canaliculi chordae

tympani) on the posterior (mastoid) wall of the middle ear’s cavity. Here, at first, the chorda

tympani runs free between the anvil (Incus) and the hammer (Malleus) and then around the

upper and anterior margin of the tympanic membrane (Membrana tympani), only covered by

the intratympanic mucosa. The nerve leaves the tympanic cavity through the petrotympanic

fissure (Fissura petrotympanica) where it meets the ascending anterior tympanic artery (A.

tympanica ant.). Exiting to the outer skull base, the nerve gains into the infratemporal region

and passing medial to the TMJ joins from posterior the lingual nerve (see there). The chorda

tympani convey preganglionar parasympathetic axons and sensorial dendrites originating in

the geniculate ganglion. The destination of the vegetative fibers is the submandibular ganglion

(Ggl. submandibulare).

The submandibular ganglion (Ggl. submandibulare) is a small peripheral nervous structure

situated between the layers of the floor of the mouth (diaphragma oris), at the posterior

margin of the mylohyoid muscle, under the lingual nerve, whom is morphologically attached.

The ganglion is made up by ganglionar („postganglionar”) neurons of the vegetative

parasympathetic division of the intermediate nerve. Similarly to the pterygopalatine ganglion,

it is morphologically bound by the means of its branches to the intermediate, the trigeminal

and the sympathetic nervous trees, but functionally and systematically belongs to the system

of the intermediate nerve only. Descriptively, two roots and efferent branches of the ganglion

are encountered.

The parasympathetic root (Radix parasympathetica) is the only proper root of the ganglion,

bringing the preganglionar axons originating in the superior salivary nucleus. As shown

previously, at first these fibers travel with the intermediate nerve, then enter the chorda

tympani nerve. After the chorda tympani becomes incorporated into the lingual nerve, the

vegetative fibers travel within the latter until reaching the submandibular region (Regio

submandibularis). Here the vegetative fibers leave the lingual nerve. Descriptively, they are

grouped in the posterior set of the Rr. ganglionares by whom they finally enter the ganglion.

The preganglionar axons synapse on the ganglionar cells, which in turn give rise to the

postganglionar axons, the efferences of the submandibular ganglion.

A sympathetic root does not occur in the case of the submandibular ganglion. This is an

exception from under the general rule of ARNOLD. Some sympathetic axons stemming in the

superior cervical ganglion (Ggl. cervicale sup.) join the nervous plexus surrounding the

external carotid artery (Plexus caroticus externus). From here they continue in a similar

plexus of the facial artery (A. facialis) and reach the submandibular gland joining the arteries.

The sensitive root (Radix sensitiva), according to the rule, is spurious. This root is represented

by trigeminal branches, the posterior set of the Rr. ganglionares of the lingual nerve. The

delicate nerves consist of sensitive dendrites originating in the trigeminal ganglion, and they

pass through the submandibular ganglion with no functional link with it.

The functional output of the submandibular ganglion turns back into the lingual nerve as the

anterior set of the Rr. ganglionares. The postganglionar axons travel for a short while with

this nerve but then some of them separate from it as the Rr. glandulares and innervate the

submandibular and the sublingual glands. Other axons travel dispersed into the sensitive

branches of the lingual nerve and innervate the small salivary glands in the floor of the oral

mucosa.

The N. VIII. or the vestibulocochlear nerve (N. vestibulocochlearis)

The vestibulocochlear nerve, also known as statoacoustic nerve, is a pure special sensory

afferent encephalic nerve composed by two distinct parts. The upper situated, vestibular part

is called the vestibular root (Radix vestibularis seu superior) as it carries the impulses of the

sense of equilibrium, acceleration and deceleration. The lower division is named acoustic root

(Radix cochlearis seu inferior), being the link to the hearing organ. It is to be mentioned, that

these so-called roots never really merge, nor are their functions related.

The proper origin is different for the two divisions. For the vestibular nerve there are three

main nuclei in the brainstem situated at the ponto-medullary border: the Nc. vestibularis sup.

(of BECHTEREW), the Nc. vestibularis med. (of SCHWALBE) and the Nc. vestibularis lat. (of

DEITERS).

The cochlear nerve’s two nuclei are described: the Nc. cochlearis ant. and the Nc. cochlearis

post. Similarly to the previous ones, the latter nuclei lie in the lateral recess of the floor of the

fossa rhomboidea (Fossa rhomboidea, Recessus lat.).

The apparent origin is in the sulcus bulbopontinus, above the bulbar olive (Oliva bulbaris),

below the middle cerebellar peduncle (Pedunculus cerebellaris medius), in the

cerebellopontine angle, antero-medial to the flocculus of the cerebellum (Flocculus). The

nerve becomes apparent lateral and posterior to the intermediate nerve.

The course of the vestibulocochlear nerve is divided into an intracranial and an intrapetrous

segment. In the posterior cranial fossa, after their apparent origin, the two functionally and

systematically distinct divisions keep allover together, forming the descriptively unitary nerve

trunk. The nerve swings anterolaterally in the cerebellopontine cistern together with the facial

and intermediate nerves. Heading the internal auditory pore (Porus acusticus int.), the nervous

setup is ensheathed by a common arachnoid envelope and it is shadowed from below by the

labyrinthic artery. Just as in the case of the facial and intermediate nerves, clinically an

intracanalar part of the vestibulocochlear nerve is distinguished inside the internal auditory

meatus.

The petrous segment commences at the bottom of the meatus, where the vestibulocochlear

nerve and the labyrinthic artery separate from the accompanying facial and intermediate

nerves. Approaching the Crista transversa of the fundus of the internal auditory meatus, the

yet apparently unitary vestibulocochlear nerve splits in its two endbranches, the acoustic and

the vestibular nerves. It is to be mentioned that there are no functional or systematic

differences between the radices and primary branches of the vestibulocochlear nerve.

Defining radices versus the primary branches is a descriptive approach only.

The anterior (or medial) division is the cochlear (or acoustic) nerve (N. cochlearis), that draws

anteroinferiorly toward the cochlear area (Area cochlearis) of the fundus and penetrates the

bony matter of the petrous part of the temporal bone. Embedded in the bone, in the spiral

canal of the modiolus of the cochlea lies the elaborate spiral ganglion (Ggl. cochleare seu Ggl.

cochleare spirale) (of CORTI), a sensorial (specific somatic sensitive) ganglion, composed of

the bipolar auditory nerve cells. Their axons bind into the cochlear nerve, whereas the

dendrites of them pass the minute holes of the Tractus spiralis foraminosus to enter the

cochlear space and there contact the sonic receptor cells.

The posterior (or lateral) branch of the vestibulocochlear nerve, the vestibular nerve (N.

vestibularis) joins the vestibular ganglion (Ggl. vestibulare) (of SCARPA) at the fundus of the

meatus. This is a sensorial (specific somatic sensitive) ganglion, nesting bipolar nerve cells.

The intrvening Crista transversa divides the ganglion into a superior and an inferior part

(Pars sup., Pars inf.). The axons of these neurons are collected in the above mentioned

vestibular nerve and run centripetally. The dendrites of the bipolar cells leave the ganglion in

two bundles that branch further. A thin branch, the R. communicans cochlearis connects the

two aformentioned ganglia.

Branches: the cochlear nerve does not form named branches. From the vestibular ganglion

stem some well defined branches, as follows:

The superior part of the vestibular ganglion is continuous in the utriculoampullar nerve (N.

utriculoampullaris). It further emits branches:

The utricular nerve (N. utricularis) directs for the innervation of the macula of the utriculus

(Macula utriculi).

The anterior ampullar nerve (N. ampullaris ant.) will connect to the receptors in the

membranous anterior semicircular canal (Ampulla canalis semicircularis ant.-is).

The lateral ampullar nerve (N. ampullaris lat.) innervates the homonimous receptor field

(Ampulla canalis semicircularis lat.-is).

The inferior part of the vestibular ganglion gives birth to two nerves:

The posterior ampullar nerve (N. ampullaris post.) targets the receptors in the ampulla of

the membranous posterior semicircular canal (Ampulla canalis semicircularis post.-is).

The saccular nerve (N. saccularis) is destined to the macula of the sacculus (Macula

sacculi).

The N. IX. or the glosopharyngeal nerve (N. glossopharyngeus)

Functionally, this is a mixed branchial motor, sensitive, sensorial and vegetative

parasympathetic efferent encephalic nerve.

Its sensitive function extends on nociception, protopathic sense, proprioception and the

specific sense of taste of the pharynx and the posterior third of the tongue.

Its branchial somatomotor branches are axons which innervate some striated muscles with

visceral and somatic functions of the pharynx (Pharynx) and of the isthmus of the fauces

(Isthmus faucium), as follows:

the superior, middle and inferior costrictor muscles of the pharynx (M. constrictor pharyngis

sup., med., inf. ), with the contribution of the X-th encephalic nerve,

the stylopharyngeus muscle (M. stylopharyngeus),

the posterior belly of the digastric muscle (M. digastricus, Venter post.) (contributes to the

facial nerve)

the levator veli palatini muscle (M. levator veli palatini),

the muscle of the uvula (M. uvulae)

the palatoglossus muscle (M. palatoglossus) and

the palatopharyngeus muscle (M. palatopharyngeus)

Its autonomous division consists of vegetative motor parasympathetic preganglionar axons.

The fibers staying within the nerve’s tree innervate glands of the pharynx. Some of the axons

leave the nerve and attach to certain trigeminal branches and innervate the parotid gland

(Glandula parotidea).

The proprioceptive component is proper to the glossopharyngial nerve tree. However,

dendritic fibers are swapped with the trigeminal system too.

The proper origin lies in the medulla (Medulla oblongata) and it is multiple:

the Nc. ambiguus - somatomotor for the aformentioned muscles,

the Nc.tractus solitarii – sensorial for the sense of taste general sensitivity, and

the Nc. salivatorius inf. - vegetative parasympathetic, origin for the preganglionar vegetative

axons

The apparent origin is the on the ventral surface of the medulla, in the sulcus retroolivarius

either directly or by the means of 2 rootlets (Fila radicularia). These typically join eachother

after a short run and form the nervous trunk.

The course of the nerve has an intracranial and a cervical segment. The intracranial segment

has a lateral course on the inner skull base. Here the nerve is situated anteromedially to the

vagus nerve and the flocculus of the cerebellum, below the vestibulocochlear and above the

hypoglossus nerves. The posterior inferior cerebellar artery (A. cerebellaris post. inf.)

stretches in between the glossopharyngeal and vagus nerves. The glosopharyngeal nerve exits

the neurocranium’s posterior fossa through the jugular foramen’s anterior, nervous part

(Foramen jugulare, Pars nervina), in the company of the encephalic nerves X and XI. In the

bony orifice the nerve encounters the entering posterior meningeal artery (A. meningea post.).

The cervical segment is much longer, and begins right under the jugular foramen. Here the

nerve is lodged in the lateropharyngeal space, anterior to the internal juglar vein (V. jugularis

int.), in lateral to the internal carotid artery (A. carotis int.), in the company of the other two

encephalic nerves with whom it exited the posterior fossa of the skull. The glossopharyngeal

nerve crosses obliquely from medial the styloid process of the temporal bone (Proc

styloideus) and then the stylopharyngeal muscle (M. stylopharyngeus), whom it joins from

lateral to form an anterior curve towards the lateral wall of the pharynx. Proceeding anteriorly,

the nerve finally is placed between the stylopharyngeal and styloglossus muscles (M.

styloglossus) and penetrates the body of the tongue (Corpus linguae) from lateral.

On its course, the glossopharyngeal nerve develops two ganglia. The first of them, the

superior ganglion (Ggl. sup.) (of EHRENRITTER) is intracranial, situated in the jugular foramen

right under the intrajugular process of the petrous part of the temporal bone (Proc.

intrajugularis). This upper ganglion is of general sensitive function, and it is built up by

pseudounipolar neurons. The inferior ganglion Ggl. inf. (of ANDERSCH) is situated

extracranially, in the Fossula petrosa. It contains pseudounipolar nerve cells also and it is

believed to be in the service of the sense of taste (viscero-sensorial specific).

Branches: the nerve gives off branches extracranially only:

The tympanic nerve (N. tympanicus) (of JACOBSON) is a small collateral twig of

parasympathetic visceral efferent function. It contains preganglionar axons. Immediately after

its origin, the nervelet enters the the petrous part of the temporal bone through the Canaliculus

tympanicus. Inside of this canal, the nerve meets the minute Ggl. tympanicum, a

parasympathetic ganglion. Some of the preganglionar axons make synapses on these

ganglionar cells, whose axons, in turn join the tympanic nerve. Traveling further in the

temporal bone, the tympanic nerve finally gains into the tympanic cavity (hence its name). On

the medial (labyrinthic) wall (Paries labyrinthicus) of the cavity the nerve spreads

exhaustively in fine branches on the Promontorium. By repeated recombinations, these

branches build up the tympanic plexus (Plexus tympanicus). Several branches emerge from

this plexus. One set of them is unnamed and contribute to the highly sensitive innervation of

the mucosa of the middle ear, including the inner, medial surface of the tympanic membrane.

Other branches are stronger and leave the tympanic cavity.

The lesser petrosal nerve (N. petrosus minor) exists the tympanic cavity trough its upper wall,

stretching in its own bony canal, the Canalis nervi petrosi minoris. This fine tunnel is

medially oriented and opens into the middle cranial fossa on the anterior surface of the the

petrous part of the temporal bone by the homonimous orifice (Hiatus canalis nervi petrosi

minoris). Here the nerve continues it medially oriented run covered by the basal dura mater,

leaving its mark on the bony surface as the Sulcus nervi petrosi minoris, then exists the

neurocranium through the Foramen lacerum or through the Foramen ovale. On the external

skull base, the nerve enters the otic ganglion, providing its parasympathetic root. (see below)

The R. tubarius enters the eustachian tube (Tuba auditiva) and innervates it mucosal lining.

The tympanic plexus receives the Nn. caroticotympanici, vegetative sympathetic nerve fibers

separated from the Plexus caroticus int. These nervelets originate in the carotid canal (Canalis

caroticus) and gain into the tympanic cavity through the homonimous foramina.

The R. communicans cum ramo auriculari nervi vagi connects the glossopharyngeal and the

vagus nerves. Function unknown.

The R. communicans cum nervo faciali connects the glossopharyngeal and the facial nerves.

It seems to be a connection through which proprioceptive fibers (dendrites) are exchanged.

The R. musculi stylopharyngei is a motor and probably proprioceptive branch for the

homonimous muscle.

The R. sinus carotici (of HERING) is an important vegetative sensitive afferent connection. It

innervates an intra-arterial receptor zone within the carotid bifurcation, the Sinus caroticus,

and a paraganglion, the carotid body (Glomus caroticum). This is a receptor organ mostly

composed of blood vessels, sensitive to changes in blood composition, pressure and

temperature.

The pharyngeal branches (Rr. pharyngei) are 3-4 nervous twigs of mixed, motor, sensitive

sensorial and vegetative function. They branch and reunite repeatadly and form a basket-like

plexus, the Plexus pharyngeus in the adventitia on the external surface of the pharynx. The

pharyngeal plexus receives similar branches from the vagus nerve (Rr. pharyngei) and

sympathetic efferents from the superior cervical ganglion (Ggl. cervicale sup.) via the carotid

plexus (Plexus caroticus). The plexus supplies the constrictor muscles of the pharynx, the M.

levator veli palatini, the M. uvulae and the M. palatopharyngeus, providing them motor and

proprioceptive innervation. Microganglia are scattered in this plexus and branches emerge

from here perforating the muscular coat for innervating the lining mucosa. These are sensorial

twigs for taste, general sensitive branches and vegetative nervelets for the small salivary

glands of the pharynx. The vault of the pharynx (Fornix pharyngis) is avoided by the

glossopharyngeal branches. It is to be mentioned that as the vagus nerve participates in the

build of the pharyngeal plexus, it concurs in the motor innervation of the pharyngeal and

palatal muscles too.

The tonsillar branches (Rr.tonsillares) are nerves for the palatine tonsil (Tonsilla palatina),

carrying sensitive and vegetative fibers. Microganglia are encountered attached to the nerve

twigs, providing secretory innervation for the small salivary glands of the mucosa lining the

tonsillar compartment.

The lingual branches (Rr. linguales) are the apparent endbranches of the glossopharyngeal

nerve of sensorial, general sensitive and vegetative function. They penetrate the tongue, and

by repeated branching and recombination form an extensive submucosal plexus, the Plexus

lingualis. Like in the above reviewed cases, this plexus contains a number of microganglia

also. Fine branches emerging from this plexus innervate the posterior (postsulcal) third of the

lingual mucosa. The sense of taste (special visceral afferents), general (somatic) sensitivity

and vegetative secretory innervation of the small lingual salivary glands is delivered by the

means of this neural meshwork.

The otic ganglion (Ggl. oticum) is a small peripheral nervous structure situated in the

infratemporal region, right underneath the foramen ovale, on the medial aspect of the

mandibular nerve, lateral to the eustachian tube (Tuba auditiva) and the M. tensor veli

palatini, posterior to the medial pterygoid muscle. This ganglion houses the ganglionar

(„postganglionar”) neurons of the vegetative parasympathetic division of the

glossopharyngeal nerve. It is morphologically linked by the means of roots and branches to

the glossopharyngeal, the trigeminal and the sympathetic nervous trees, but functionally and

systematically belongs to the glossopharyngeal system only. According to ARNOLD’s rule,

from the point of view of the systematic anatomy, as the cephalic parasympathetic ganglia

generically, the otic ganglion has three roots and one set of branches. Out of the three roots

one is real, with functional value, the other two are spurious.

The parasympathetic root (Radix parasympathetica), conveying the preganglionar axons, is

the only proper root of the ganglion, originating in the Nc. salivatorius inf. This emerges from

the above mentioned lesser petrosal nerve. The preganglionar axons synapse on the ganglionar

cells, which in turn give rise to postganglionar axons, the output of the otic ganglion.

The sympathetic root (Radix sympathetica) (or n. petrosus prof. min.) only apparently belongs

to the ganglion, because, in fact, these axons merely transit it. They stem in the superior

cervical ganglion (Ggl. cervicale sup.) of the cervical sympathetic chain, and approach this

ganglion via the nervous plexus surrounding the internal carotid artery (Plexus caroticus

internus). A set of nervelets are described to split off this plexus and approach the otic

ganglion. The fibers pass the otic ganglion without making any functional connection with it

and join the vegetative branch emerging from here, the R. communicans cum nervo

auriculotemporali.

The sensitive root (Radix sensitiva) is represented by two trigeminal branches, passing

through, but functionally not linked to the ganglion. They originate from the auriculotemporal

nerve (N. auriculotemporalis), a branch of the mandibular nerve (N. mandibularis), which in

turn is a primary branch of the trigeminal nerve (N. trigeminus). These nervelets are partly

sensitive, built up by some peripheral dendrites dispatched from the trigeminal sensitive

ganglion (Ggl. trigeminale), but also contain efferent axons stemming in the motor nucleus of

the trigeminus. These come to the ganglion through the motor root of the trigeminal nerve

(Radix motoria n.-i trigemini). Obviously, these fibers do not synapse in the otic ganglion.

Rather, they separate as thin communicating twigs to the N. tensoris palatini and the N.

tensoris tympani. These latter nerves can appear as originating from the otic ganglion.

The main emerging branch of the otic ganglion is the R. communicans cum nervo

auriculotemporali, carrying the postganglionar parasympathetic axons to the trigeminal

system. They provide the secretory innervation of the parotid gland (Gl. parotis) (see the

auriculotemporal nerve). However, other smaller branches are dispatched also. The R.

communicans cum nervo buccali seemingly transports postganglionar axons to this nerve for

the innervation of the small salivary glands of the oral vestibule. The R. communicans cum

ramo meningeo links the otic ganglion with the meningeal branch of the mandibular nerve,

contributing perhaps to the vegetative innervation of the meninges of the middle cranial fossa.

The R. communicans cum nervo chorda tympani is a communication to the system of the

intermediate nerve, of uncertain functional importance.

The N. X. or the vagus nerve (N. vagus)

Functionally, this is a mixed branchial motor, sensitive and vegetative afferent and vegetative

parasympathetic efferent encephalic nerve. The nerve’s once attributed sensorial function

(taste) is doubted in adult.

Its sensitive function extends on nociception, proprioception as well as the vegetative, less

conscious sense of chemical, osmotic, thermal or pressure changes in the internal environment

(“millieu interieur”) of the body.

Its branchial somatomotor branches are axons which innervate the striated muscles of

visceral functions of the pharynx (Pharynx), larynx (Larynx) and of the upper third of the

esophagus (Esophagus), as follows:

the cricothyroid muscle (M. cricothyroideus),

the posterior cricoarytenoid muscle (M. cricoarytenoideus post.),

the lateral cricoarytenoid muscle (M. cricoarytenoideus lat.),

the vocalis muscle (M. vocalis),

the thyroarytenoid muscle (M. thyroarytenoideus)

the oblique arytenoid muscle (M. arytenoideus obliquus) and

the transverse arytenoid muscle (M. arytenoideus transversus)

Its autonomous division consists of vegetative motor parasympathetic preganglionar axons.

Their function includes innervation of all the possible vegetative effectors, namely glands and

smooth muscles.

The proprioceptive component is obviously extant, but less well understood. It is also likely

that the vagus provides proprioceptive innervation for striated muscles whose motor

innervation is accomplished by other nerves.

The proper origin lies in the medulla (Medulla oblongata) and it is multiple:

the Nc. ambiguus - somatomotor for the aformentioned muscles,

the Nc.tractus solitarii – sensitive for the sense of general sensitivity, and perhaps for the

visceral sessitivity too

the Nc. salivatorius inf. – preganglionar vegetative parasympathetic secretomotor for the

lower pharyngeal, the laryngeal and the esophageal glands

the Nc. dorsalis n.-i vagi. – preganglionar vegetative parasympathetic, origin for the

preganglionar vegetative axons innervating smoth muscels and glands of the visceral organs

The apparent origin is the on the ventral surface of the medulla, in the sulcus retroolivarius

by the means of 8-10 rootlets (Fila radicularia), beween the rootlets of the glossopharyngeal

and the accessory nerves. These filaments merge after a short lateral run and form the nervous

trunk of the vagus.

The course of the nerve is very long, asimmetrical on the midline and divides into 6

segments. Up to the entrance in to the thorax, the Apertura thoracalis sup., the left and right

vagus nerves have similar syntopy. Inside the mediastinum (Mediastinum) and further down

in the abdomen striking differences are met.

The intracranial segment has a lateral course on the inner skull base. Here the nerve is

situated posterolaterally to the glossopharyngeal nerve and anterior to the flocculus of the

cerebellum, below the vestibulocochlear and above the hypoglossus nerves. As already

shown, the posterior inferior cerebellar artery (A. cerebellaris post. inf.) stretches in between

the glossopharyngeal and vagus nerves.

The cranial segment is the shortest, being that part of the nerve by which vagus nerve exits the

neurocranium’s posterior fossa. The passageway is the jugular foramen’s antero-medial,

nervous part (Foramen jugulare, Pars nervina), shared between the encephalic nerves IX, X

and XI. In the bony orifice the nerve encounters the entering posterior meningeal artery (A.

meningea post.) and one of its own branches, the entering posterior meningeal nerve (N.

meningeus post.).

The cervical segment is much longer, and begins right under the jugular foramen. Here the

nerve is lodged in the retrostylic compartment of the lateropharyngeal space (Spatium

lateropharyngeum), anterior to the internal juglar vein (V. jugularis int.), lateral to the

pharynx and the internal carotid artery (A. carotis int.), in the company of the other two

encephalic nerves with whom it exited the posterior fossa of the skull. The nerve is also

accompanied by the main lymphatic ways of the neck (Truncus lymphaticus jugularis dexter

et sinister) and some of its own branches: throughout its cervical descent by the upper cervical

cardiac branches (Rr. cardiaci cervicales superiores) and down to the thyroid cartilage

(Cartilago thyroidea) by the superior laryngeal nerve (N. laryngeus sup.), all these emitted

just under the outer skull base. Surpassing the styloid diaphragm (Diaphragma stylica), the

nerve enters the region of the carotid trigone (Regio trigonum caroticum). Here it descends

anterior to the prevertebral sympathetic chain (Truncus sympathicus, Pars cervicalis), lateral

to the larynx (Larynx) and the esophagus (Esophagus), medial to the internal jugular vein and

posterior to the common carotid artery (A. carotis communis), enveloped together with these

large vessels by the carotid sheath (Vagina carotica). Then, below the cricoid cartilage

(Cartilago cricoidea) the nerve is to be found in the sternocleidomastoid region (regio

sternocleidomastoidea) lateral to the trachea (Trachea), maintaining its position to the great

vessels of the neck. Here the nerve passes close and parallel to the posterior edge of the

corresponding lobe of the thyroid gland (Glandula thyroidea). At the root of the neck the

syntopy of the vagus nerve changes. It is placed medial to the phrenic nerve (N. phrenicus),

posterior to the great veins and anterior to the great arteries, being crossed from anterior by

the subclavian vein (V. subclavia) and from posterior by the subclavian artery (A. subclavia).

On the right side it also comes in contact with the inferior cervical ganglion of the

sympathetic chain (Ggl. cervicale inf., or, in case, the Ggl. cervicothoracicum). On the left

side the nerve is crossed from lateral by the thoracic duct (Ductus thoracicus). Below, the

nerve is pushed anteriorly by the pleural dome (Cupula pleurae) which is its posterior.

The thoracal segment begins where the nerve passes inferiorly through the superior thoracal

opening (Apertura thoracalis superior). In the thorax the nerve descends in the mediastinum

and branches exhaustively. The endbranches of the nerves from the both sides recombine and

form an elaborate plexus surrounding the esophagus (Plexus esophageus). This plexus

contains nervous fibers of all functional types. From this plexus direct branches are sent off

for the innervation of the thoracal organs and finally, in the inferior posterior mediastinum

two main nervous trunks collect from the remaining esophageal plexus. These are the anterior

and the posterior vagal trunks (Truncus vagalis ant. et post.).

The diaphragmatic segment refers to the short passageway across the diaphragm

(Diaphragma) and concerns not the vagus nerves, but the resulting vagal trunks (Truncus

vagalis) only.

The abdominal segment is in fact retroperitoneal. From here the vagal branches may enter the

mesos to reach the target organs if they are intraperitoneal or search the retroperitonal organs

directly.

On its course, the vagus nerve develops two ganglia. The superior ganglion is the smaller,

shperical (Ggl. sup.) (Ggl. jugulare) situated extracranially, inferior the jugular foramen. This

ganglion has communicating branches with the VII-th, IX-th and the XI-th encephalic nerves.

The inferior ganglion (Ggl. inf.) (Ggl. nodosum) is larger, fusiform. This ganglion is linked by

the means of faint nervous loops with the XII-th encephalic nerve and with the cervical

sypmathetic chain.

Branches: the nerve gives off branches extracranially only:

The posterior meningeal nerve (N. meningeus post.) is a thin collateral sensitive twig,

stemming at the level of the superior ganglion. It turns upwards and penetrates the posterior

cranial fossa through the jugular foramen for innervating the meninges.

The auricular branch (R. auricularis), sensitive, also emerges from the superior ganglion. It

courses posteriorly for a short while and enters its own bony canal (Canaliculus mastoideus)

in the jugular fossa (Fossa jugularis). Te nervelet travels in the sinuous canal till its inferior

openig, the tymapnomastoid fissure (Fissura tympanomastoidea). It splits in two endbranches

and innervates the skin of the posterior side of the external auditory meatus (Meatus acusticus

ext.) and the skin of the back of the auricule (Auricula).

The R. communicans cum nervo glossopharyngeo creates a link to the XI-th encephalic

nerve.

The pharyngeal branches (Rr. pharyngei) are released from the inferior ganglion and in

addition to sensitive fibers (dendrites), contain motor fibers furnished by the accessory nerve

and vegetative efferents of the vagus’s owns. The nerves descend and curve anterior crossing

from medial the internal and then the external carotid arteries to reach the lateral wall of the

pharynx. Here they split in branches which combine with the pharyngeal plexus’s (Plexus

pharyngeus) other fibers of glossopharyngeal origin. The vagus nerve, by these fibers of

accessorial provenance innervates mainly the inferior constrictor muscle (M. constrictor

pharyngis inf.) and probably contributes to the motor innervation of the other pharyngeal

constrictor muscles too. The sensitive component of these nerves innervates the mucosa of the

hypopharynx (Hypopharynx), whereas the vegetative twigs act on the small salivary glands of

the same area. It is assumed that the muscles of the soft palate (Palatum molle), except the M.

tensor veli palatini also share in the vagal innervation.

The recurrent nerve (N. [laryngeus] recurrens) is a mixed, motor, sensitive and probably a

vegetative efferent nerve with different origin and course on the two sides. The right inferior

laryngeal nerve originates where the right vagus nerve crosses from anterior the right

subclavian artery (A. subclavia dextra). Then it surrounds this artery from below to posterior

and begins to ascend on the right side of the neck in the groove formed between the trachea

and the esophagus. The nerve travels in the close proximity of the medial side of the right lobe

of the thyroid gland (Lobus dexter glandulae thyroideae) upward to the larynx. The left

inferior laryngeal nerve begins more inferiorly, where the left vagus nerve crosses the aortic

arch (Arcus aortae) anteriorly. From here, the nerve ascends on the left side of the neck, in the

groove between the trachea and esophagus, more hidden than the other side due to the

rightward deviation of the esophagus. The syntopy established with the left lobe of the thyroid

gland (Lobus dexter glandulae thyroideae) is identical as on the other side. The recurrent

nerve branches exhaustively giving off twigs lateral to the trachea and on the larynx. As

shown, the recurrent nerve is morphologically linked with the superior laryngeal nerve.

The inferior laryngeal nerve or (N. laryngeus inf.) is the direct continuation of the recurrent

nerve. It penetrates the cricothyroid membrane and provides motor innervation for the major

part of the laryngeal muscles: the posterior cricoarytenoid muscle (M. cricoarytenoideus

post.), the lateral cricoarytenoid muscle (M. cricoarytenoideus lat.), the vocalis muscle (M.

vocalis), the thyroarytenoid muscle (M. thyroarytenoideus) the oblique arytenoid muscle (M.

arytenoideus obliquus) and the transverse arytenoid muscle (M. arytenoideus transversus).

The inferior laryngeal nerve also innervates the mucosa of the larynx inferior to the glottis,

supplying it sensitive innervation and probably vegetative motor innervation of its small

glands. The tracheal branches (Rr. tracheales) are intended for the innervation of the

mucosa of the trachea (sensitive, secretory) and possibly for the motor innervation of the M.

trachealis (vegetative motor) also.

The esophageal branches (Rr. esophageales) furnish sensitive and probably secretomotor

innervation for the uppermost part of the esophageal mucosa and the included glands. The

pharyngeal branches (Rr. pharyngeales) join the pharyngeal plexus (Plexus pharyngeus)

carrying fibers of all types: motor, sensitive and vegetative secretomotor.

The superior cardiac branches (Rr. cardiaci cervicales supp.) are usully detached just

below the inferior ganglion. They also can be released from the superior laryngeal nerves.

After their origin, these branches join the internal carotid artery and then the common carotid

artery. Further down the nerve on the right descends in the front of the brachiocephalic trunk

(Truncus brachiocephalicus) until the aortic arch (Arcus aortae). The nerves of both sides

split in branches which unite in the front of the aorta as the cardiac plexus (Plexus cardiacus).

This plexus will be joined by other branches of the vagus nerves (the inferior cardiac

branches) and by twigs of the cervical sympathetic chain.

The inferior cardiac branches (Rr. cardiaci cervicales inff.) are 1-2 twigs broadcasted from

the vagus nerve or from the recurrent nerve. Descending together with the superior cardiac

branches, the inferior ones have the same fate and destination, namely to break off in branches

which in turn enter the cardiac plexus. It is to be mentioned that the right vagus has a major

functional importance in the innervation of the heart.

The anterior and posterior bronchial branches (Rr. bronchiales antt. et postt.) are delicate

nerves of sensitive, secretomotor and visceral motor vegetative function. They are dispatched

in the mediastinum, from the thoracal segment of the vagus nerve, where it crosses from

anterior the principal bronchus (Bronchus principalis). These branches soonish dissipate by

breaking off into fine branches which travel along the bronchial tree and provide sensitive

innervation for the bronchial and pulmonar mucosae, vegetative secretomotor innervation for

the small mucosal glands as weel as the crucially important visceromotor innervation of the

smooth muscles of the bronchioli (Bronchioli). The vagal twigs are mixed with branches

stemming from the cevical sympathetic chain to form the pulmonary plexus (Pl. pulmonalis).

The esophageal branches (Rr. esophagei) are mixed nerves of sensitive and visceromotor

function. These nerves separate from the esophageal plexus (Pl. esophageus) and innervate

the mucosa of the esophagus in its lower 2/3-s (sensitively), its small glands (secretomotor)

and the muscular coat (visceromotor).

The gastric branches (Rr. gastrici) are mixed nerves of viscerosensitive, secretomotor and

visceromotor function. They are broadcasted in the retroperitoneum from the abdominal

segment of the vagus. However, instead of being branches of the vagus nerve, they stem from

the vagal trunks. The nervelets join the arteries of the stomach and innervate the mucosa with

sensitive afferents, the gastric glands with secretomotor efferents and for a lesser extent the

gastric smooth muscles with visceral motor efferents.

The celiac branches (Rr. celiaci) are functionally mixed twigs broadcasted in the

retroperitoneum. As the previous sets of branches, these are also of viscerosensitive,

secretomotor and visceromotor nature. The endbranches of the two (anterior and posterior)

vagal trunks mix in the visceral nervelets. Microganglia are described upon their course and

the vagal twigs are joined by sympthetic efferent fibers originating from the thoracal and the

abdominal sympathetic chain. The fine nervous fibers advance together with the arteries of the

abdominal organs to the liver (Hepar), the biliary vesicle (Vesicula biliaris), the pancreas

(Pancreas) the duodenum (Duodenum), the lesser intestine (Intestinum tenue), the kidney

(Ren) and the renal pelvis (Pelvis renalis). Similar nervelets innervate the colon (Colon seu

Intestinum crassum) on its proximal part, down to the left 1/3-rd of the transvese colon (Colon

transversum). Here, at the CANNON – BOEHM’s point the innervation of the digestive tract is

taken over by the sacral parasympathetic.

It is to be mentioned that the vagus’ effect on the innervation of the internal organs is

eminently secretory, with a certain but lesser involvement in the peristaltic motions. The

sensitive innervation is of vegetative type, diffuse and less conscious.

The N. XI. or the accessory nerve (N. accessorius)

The acessory nerve is a somitic somatomotor efferent encephalic nerve. It is unique among the

encephalic nerves by the fact that it originates from two distinct parts of the neuraxis, from the

medulla (Medulla oblongata seu Bulbus encephali) and the spinal chord (Medulla spinalis).

The main part of the nerve only innervates the trapezius and the sternocleidomastoid muscles

(M. trapezius), (M. sternocleidomastoideus). However, at its beginning, the nerve hosts much

different fibers, regarding both their origin and their function: branchial visceromotor

efferents. This component is soonish ceded to the nerve where it truly belongs, the vagus

nerve.

The proper origin lies in the medulla, in the ambiguus nucleus (Nc. ambiguus) and the

ventral horn (Cornu ant.) in the 1-6 cervical segments of the spinal chord. This latter part of

the spinal grey matter is the direct caudal continuation of the Nc. ambiguus.

The apparent origin is situated in the lower third of the retroolivar groove of the medulla

(sulcus retroolivarius) and its downward continuation on the spinal chord, the Sulcus postero-

lat. The encephalic part of the nerve begins with 3-6 rootlets (Fila radicularia), joined

together in the cranial root (Radix cranialis n.-i accesssorii) (Pars vagalis). The spinal

component stems with up to 6 groups of rootlets, united by the longitudinal spinal root (Radix

spinalis n.-i accessorii). The spinal root climbs on the lateral surface of the spinal chord and

enters the Foramen magnum behind the vertebral artery (A. vertebralis) to join the cranial

root.

The course of the accessory nerve is divided in an intracranial and an extracranial segment.

The intracranial segment commences where the nerve itself begins: lateral to the medulla, in

the proximity of the Foramen jugulare, where the two roots merge to form the bulk of the

nerve (Truncus n.-i accessorii). The nerve exits the posterior cranial fossa in the company of

the vagus nerve through the jugular foramen.

The extracranial segment begins just under the outer skull base (Basis cranii ext. seu

Exobasis). The nerve is placed anterior to the internal jugular vein, posterior to the internal

carotid artery and lateral to the glossopharyngeal, vagus and hypoglossus nerves. Here the

accessory nerve immediately splits into its two endbranches.

Branches: the nerve emits o collateral branches, instead it bifurcates right below the

jugular foramen into an internal and an external branch.

The internal branch (R. internus) is short and joins the vagus nerve. It carries the

branchial visceromotor efferent component of the accessory nerve, originating in its

encephalic nucleus. These fibers will be broadcasted as the vagus’ owns to the larynx and the

hypopharynx, for the striated muscles located there. This branch, regarding its real origin and

destination behaves as an aberrant division of the vagus nerve.

The external branch (R. externus) is composed of the spinal division of the accessory

nerve. It has an oblique, posterior and lateral course and crosses the occipital artery (A.

occipitalis). The nerve approaches from medial the upper insertion area of the

stranocleidomastoid muscle and travels further posteriorly on its deep surface. Then it reaches

the deep (anterior) surface of the trapezius muscle and descends obliquely covered by the

lateral margin of this. The nerve gradually tapers emitting muscular branches to these muscles

(Rr. musculares). This branch ends at approximately two fingerwidths above the clavicle

(Clavicula) where its last muscular branch vanishes by penetrating the muscular mass of the

trapezius.

The N. XII. or the hypoglossal nerve (N. hypoglossus)

The hypoglossal nerve is a somitic somatomotor efferent encephalic nerve. Its endbranches

contain proprioceptive fibers also, but they are transferred to other cranial nerves with

sensitive function. This nerve innervates the muscles of the tongue, all of the intrinsic ones

and several of the extrinsic ones, as follows:

the genioglossus muscle (M. genioglossus),

the hyoglossus muscle (M. hyoglossus),

the styloglossus muscle (M. styloglossus),

the superior longitudinal muscle of the tongue (M. longitudinalis sup.),

the inferior longitudinal muscle of the tongue (M. longitudinalis inf.),

the transverse muscle of the tongue (M. transversus linguae) and

the vertical muscle of the tongue (M. verticalis linguae) and, additionally

the geniohyoideus muscle (M. geniohyoideus).

The proper origin lies in the medulla, in the hypoglossal nucleus (Nc. n.-i hypoglossi).

The apparent origin is situated in the preolivar groove of the medulla (sulcus preolivarius)

with 10-15 rootlets (Fila radicularia), joined together in the trunk of the nerve.

The course of the hypoglossal nerve is divided in an intracranial, a cranial and a cervical

segment. The intracranial segment, situated in the posterior cranial fossa, commences where

the nerve itself begins: anterolateral to the medulla, where the rootlets fuse to form the bulk of

the nerve. Thence, the nerve draws laterally, posterior to the vertebral artery (A. vertebralis)

that it crosses.

Entering its own bony canal, the Canalis nervi hypoglossi, the nerve is to be found in its

second, cranial segment, being accompanied by a satellite vein and the appended venous

plexus (V. canalis hypoglossi). Here a vestigial, rudimentar artery, the hypoglossal artery (a.

hypoglossica) might be also present, anastomotically linking the external and internal carotid

arterial systems.

The cervical segment begins under the outer skull base (Basis cranii ext. seu Exobasis). Here

the hypoglossal nerve is placed anterior to the internal jugular vein, posterior to the internal

carotid artery and lateral to the glossopharyngeal and the vagus nerves and medial to the

accessory nerve. Here the hypoglossal nerve receives a communicating nervous trunk built up

by some somatomotor branches issued by the 1-st and the 2-nd cervical spinal nerves.

Enriched with these fibers only temporally, the nerve winds forward and descend following

for a while medially the posterior belly of the digastric muscle (Venter posterior, M.

digastricus). Then the nerve arches to variable extent below this muscle and around the

commencement of the occipital artery (A. occipitalis), then crossing from lateral the external

carotid (A. carotis ext.) and the lingual (A. lingualis) arteries penetrates the vertical slit

between the hyoglossus and mylohyoideus muscles (M. hyoglossus, M. mylohyoideus).

Branches: the nerve discards the fibers accepted from the first two cervical spinal nerves,

gives off muscular twigs, establishes connections by the means of communicating branches

and ends by being dispersed in the tongue.

The superior root of the cervical loop (Radix sup. ansae cervicalis (profundi))

equals the descendent cervical branch of the hypoglossal nerve and is detached in the carotid

triangle (Regio trigonum caroticum). This is a connection to the system of the cervical plexus

(Plexus cervicalis), containing somatomotor efferents (axons) from the upper two cervical

segments of the spinal chord. This bundle is completed from below by the inferior root of the

cervical loop (Radix inf. ansae cervicalis (profundis)) built up by some ascending fibers

originating from the 2-nd and the 3-rd cervical spinal nerves. The upper and the lower roots

unite in the Ansa cervicalis (profunda) at the level of the intermediate tendon of the omohyoid

muscle (M. omohyoideus), lateral to the common carotid artery (A. carotis comm.). From the

convexity of this nervous complex, muscular branches are issued for the motor (somitic

somatomotor and perhaps proprioceptive too) innervation of the infrahyoid muscles: M.

thyrohyoideus, M. sternothyroideus and M. sternohyoideus. As demonstrated, functionally and

systematically these fibers are not of the hypoglossal nerve’s own, they are just parasitising it.

The Ansa cervicalis (profunda) should be differentiated to the Ansa cervicalis (superficialis),

a belonging of the facial nerve.

The lingual branches (Rr. linguales) are the muscular branches of the nerve for the

muscles listed above, providing a strictly unilateral innervation. Proprioceptive dendrites are

also hosted in these otherwise efferent twigs. After a short run, these dendrites are ceded to

where they belong, the trigeminal system. (see below)

The communicant branches (Rr. communicantes) contain the nerve fibers exchanged

with other nerves. These include the cervical plexus, the upper cervical sympathetic ganglion,

the vagus nerve and the lingual nerve. (see above)