Transcript Skeletons •All the struts, none of the ties; strut resists compression, tie resists tension •“the form of an object is a diagram.

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
Univ of Wisconsin
• 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
Transverse section Lumbricus
Coelom: fluidfilled 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