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

Flatworms Phylum Platyhelminthes locomotion by cilia and body waves

Christmas Tree worms, Phylum Annelida

From Wikkimedia Commons pictures by Hans Hillewaert Nereis succinia epitoke of polychaete worm

Phylum Annelida mostly marine Lumbricus earthworm 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 geographic Landing is also important and pectoral girdle reflects design to dissipate kinetic energy of jump