Skeletons All the struts, none of the ties; strut resists compression, tie resists tension “the...

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 are forces), joints (of bones and leg segments), 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

• Leg segments, cylinders of exoskeleton, 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

Coelom: fluid-filled cavity formed in mesoderm, functions as hydrostatic skeleton to translocate forces generated by circular and longitudinal muscle antagonists

Rana skeleton: modifications for jumping (saltatorial adaptation): pelvic girdle: pubis, ischium, ileum; see urostyle. ‘tarsal bones’ just beyond ankle

joint

Gastrocnemius or[= plantaris] muscle: originates on femur and inserts on bones beyond the ankle joint; its contraction contributes to extension of limb

Frog’s legs (Rana catesbeiana, bullfrog ) ready for the chef: note the gastrocnemius and white associated Achilles’ tendons

Marinex Co.(Seafood) Taiwan

Picture credit: National geographicLanding isalso important and pectoralgirdle reflectsdesign to dissipatekinetic energy of jump