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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