CHORDATA 



33^ 



6. Caudal vertebrae, posterior to the sacrum and possessing 

 no ribs. 



The number of bones in these regions is very variable in 

 the phylum as a whole, but, in the higher forms particularly, 

 individuals of related species present remarkable uniformity. 



(The discussion of the condition of the skull and the origin of its parts is entirely 

 too technical for an elementary text. The student should refer to rriore advanced 

 works.) 



Fig. 159. 



Fig. 159. Diagram of veterbrae ol a bony fish. ^1. caudal; B, trunk, t, centrum or body of 

 the vertebra; ch., the notochord; A. a., haemal arch; h.c, hsemal canal; h.s., hsemal spine; h.z., hfemal 

 Eygapophysis, or articulating facet; m.b., inter-muscular bone; n.a,, neural arch; n.c, neural canal; 

 n.s., neural spine; n.z.t neural zygapophysis; r, rib. 



Questions on the figures. — What is the meaning of hsemal? Of neural? In 

 life what occupies the neural canal? What occupies the hsemal canal in the caudal 

 region? In the trunk region? Is there anything to suggest that the ribs in fishes 

 are homologous with the processes which form the haemal arch (h.a.) ? 



350. The Appendicular Skeleton. — Here are embraced the 

 skeletal parts of the appendages proper, together with the bones 

 binding them to the axial skeleton (girdles). Each girdle may 

 be said to consist typically of three bones, uniting to form a joint 

 with the first bone of the limb. One of these is dorsal and the 

 others ventral (Fig. i6i, B; il, is, p.). The appendages are 

 much alike both as to their girdles and the limbs proper. The 

 posterior is, in higher forms, more intimately fused with the 

 axial skeleton, thus securing greater strength at the expense of 

 freedom of motion. The first joint of each appendage consists 

 of one bone (arm or thigh); the second, of two (forearm or 



