422 



THE RABBIT. PHYLUM CHORDATA 



is small. The movement of the joint is brought about by the 

 contraction of muscles ; the end of a muscle attached to a 

 relatively fixed point is its origin, that attached to a movable 

 one its insertion. Muscles are fastened to bones by means of 

 tendons. 



In the embryo the skeleton is first formed in cartilage or gristle 

 (p. 517), but for the most part this is replaced by the harder 



V.L 



cm. 



Fig. 335. — The skeleton of a rabbit. 



acr., Acromion ; cd.t., condyles for tibia ; cm., calcaneum ; cn.c, cnemial crest ; fe., shaft of femur ; fi., 

 fibula ; g.L, great trochanter ; gr.t., premolar and molar teeth ; h., head of humerus, fitting into glenoid 

 cavity ; hu., shaft of humerus ; il., ilium ; inc., upper incisor teeth of the left side ; inc',, lower incisor 

 tooth ; is., ischium ; ju., jugal bone ; lac, lacrimal bone ; mcr., metacromion ; mx., maxilla ; o.f., 

 obturator foramen ; ol., olecranon process ; os., orbitosphenoid bone ; pa., knee-cap ; pis., pisiform 

 bone ; pu., pubis ; ra., radius ; sc, scapula ; sp.s., spine of scapula ; st., sternum ; st.r., sternal ribs ; 

 sup., suprascapular ; t.^, third trochanter ; ti., tibia ; tro., trochlea ; ul., ulna ; v.cd., v.cer., v.l., v.sac., 

 v.th., caudal, cervical, lumbar, sacral, and thoracic regions of the backbone ; v.r., vertebral ribs ; 

 X., xiphistemum ; x.c, xiphoid cartilage ; //., foramen for optic nerve. The clavicle and hyoid are 

 not shown. Enlarged views of the parts of the skeleton are given in the succeeding figures. The limbs 

 and ribs of the left side only are shown. 



and more durable bone (p. 518). Cartilage persists on the surfaces 

 of joints and in a few other places. In the skull and the shoulder 

 girdle there are, in addition to the cartilage bones formed in 

 (but not from) cartilage, other sets called membrane bones. These 

 are really part of an exoskeleton which has sunk inwards from 

 the skin. Small bones are also formed in other tissues. 



BACKBONE 



Each vertebra (Fig. 336) is entirely bony and consists of a body 

 or centrum with above it a neural arch which encloses a vertebral 

 foramen, surmounted by a neural spine or spinous process. Each 

 arch bears in front an upward-facing facet or anterior articular 

 process or prezygapophysis, and behind a downward-facing 



