Muscles of mandible

By: Abdul Muhaimin (D11 A007)Reference: Veterinary anatomy of domestic animal

(Book)

Mandibular muscles

• Comprise muscle of mastication and superficial muscles of mandibular space.

• Innervated by mandibular nerve (trigeminal nerve)

• Responsible for movement jaw (mastication)

• Covers mandibular space and hyoid apparatus ventrally.

• Different species have their own structure of muscle for mastication.

Mandibular muscle

• Muscle of mastication– Masseter muscle– Medial and lateral pterygoid muscles– Temporal muscle

• Superficial muscles of mandibular space– Digastric muscle– Mylohyoid muscle

• Masseter muscle– Broad multipennate muscle– Multiple tendinous intersections

• Origin– From ventral border of zygomatic arch and facial crest

• Insertion– On the lateral aspect of mandible

• Extend– From facial notch to temporomandibular joint.

Muscle of mastication

• In carnivores, it is separated into 3 layers – Superficial, middle, deep (by tendinous sheets)

• Superficial portion is the strongest• Middle layer is the weakest• In pig, these three layers are firmly fused• Tendinous intersections are pronounced, forming 5

distinct parts in the ox.• Change in fibre direction between each portion

increases masticatory force of this muscle

Masseter muscle

• In horse, it shows up to 15 tendinous intermuscular strands which are orientated sagitally and divide muscle into multiple layers.

• Both sides masseter muscles act together will force upper and lower jaw together

• Mandible can be move to the side of contracting muscle (grinding in herbivores)

Masseter muscle

• Pass from palatine, pterygoid and sphenoid bones to the medial aspect of mandible.

• Lateral pterygoid muscle is smaller than medial one.

• In carnivores, both are fused at their origin• Horse: medial pterygoid muscle is covered by

lateral one. Mandibular nerve passes across lateral surface of medial pterygoid muscle (separating 2 pterygoid muscles).

Pterygoid muscle

• Pterygoid and masseter muscles contract bilaterally will raise mandible, but if working unilaterally, will draw mandible to side of contracting muscle.

• Lateral portion also able to move mandible rostrally (mouth open)

Pterygoid muscle

• Size varying in different species depending size fossa

• The strongest muscle of head in carnivores.• Dolichocephalic dogs: temporal muscle meets

corresponding muscle of opposite side in midline (form mid-line sulcus)

• Brachycephalic dogs: two muscles don’t meet, no sulcus visible

Temporal muscle

• Ruminant: temporal muscle is indistinct but visible in horse

• Horse: temporal muscle however do not well developed compared to other masticatory muscles.

• It raises mandible acting together with other masticatory muscles.

Temporal muscle

• Assist muscles of mastication. Cover ventral side of lingual muscles in mandibular space.

• Digastric muscle– Single bellied muscle in domestic animal (except

horse)– Horse: has caudal and rostral bellies– Other domestic mammals: evolutionary bipartite

structure is indicated by a fibrous intersection.

Superficial muscle of mandibular space

• Rostral part is innervated by mylohyoid nerve (branch of mandibular nerve)

• Caudal part by digastric branch of facial nerve• In carnivores: it is strong single-bellied muscle

with delicate tendinous strands (mark division between rostral and caudal portion)

• Ruminants: tendinous intersection between two bellies is indistinct.

• Horse: rostral belly depresses mandible and opens mouth

Digastric muscle

• Form sling between inner surface of body of mandible

• Innervated by mylohyoid nerve (branch of mandibular nerve), assigned to mandibular group

• Can also be seen as lingual muscle (its function)

• Supports tongue and raises it towards palate

Mylohyoid muscle