Skeletons

• All the struts, none of the ties; strut resists compression, tie resists tension•“the form of an object is a diagram of forces”; translocation of forces (tensions, compressions),

joints, origins and insertions: • Three skeletal forms: hydrostatic, endoskeleton, exoskeleton• Examples: Frog leg; insect mandible; segmented worm coelom

• Frog: femur, tibiofibula, astralagus (ankle); gastrocnemius, Achilles’ tendon etc.• Grasshopper cranium: adductor and abductor apodemes

•Appendage movments: adduction vs abduction; promotor vs remotor, depressor vs elevator, extensor vs flexor, retractor vs protractor

• Annelida: leech looping locomotion; why are earthworms metameric? coelom, peristaltic burrowing: outer circular, inner longitudinal muscle; incompressible coelomic fluid etc.; flatworm

in a burrow?• Unshortening muscles:

• Anatagonists : tibialis anticus longus vs plantaris; adductor mandibular muscle vs abductor mandibular muscle; circulars vs longitudinals

• Elastic energy storage; scallop hinge; abductin, resilin•Pinnate fibre arrangement on blade apodeme: plantaris (gastrocnemius), mandibular adductor

etc: high force, short distance• Muscles of frog jump: elasticity influences muscle operating length

• Shock absorbers: cartilage: pectoral girdle frog• Synovial fluid: lubrication

• Joint planes change proceeding distally on crayfish claw, half-moon membranes

Endoskeleton and frog jump; exoskeleton and chewing

FlatwormsPhylum Platyhelmintheslocomotion by cilia and

body waves

Christmas Tree worms, Phylum Annelida

From Wikkimedia Commonspictures by Hans Hillewaert

Nereis succinia epitoke of polychaete worm

Phylum Annelidamostly marine

Lumbricusearthworm

• The adaptiveness of a segmented body: outer circular and inner longitudinal muscles, septa (septum sing.) fore and aft compartmentalize the coelom; muscles made antagonists by the fluid skeleton: the coelomic fluid, which translocates forces; moving in a burrow

Univ of Wisconsin

Transverse section Lumbricus

Frog’s legs ready for the chef: note the gastrocnemius and white associated Achilles’ tendons