CHORDATA. 



327 



1. Head region (skull) embracing the cranium or brain 

 case and its associated ventral arches including the bones of 

 the face. 



2. Cervical vertebrae, located in the neck and lacking ribs. 

 Usually the anterior one or two are considerably modified. 



FIG. 157. 



-n.s. 



FIG. 157. Diagram of vertebrae of a bony fish. A, caudal; B, trunk, c, centrum or 

 body of the vertebra; ch., the notochord; h.a., haemal arch; h.c., haemal canal; h.s., 

 haemal spine; h.s., haemal zygapophysis, or articulating facet; m.b., inter-muscular 

 bone; n.a., neural arch; n.c., neural canal; n.s., neural spine; n.z., neural zygapophysis; 

 r, rib. 



Questions on the figure. What is the meaning of haemal ? Of neural ? 

 In life what occupies the neural canal ? What occupies the haemal canal in 

 the caudal region ? In the trunk region ? Is there anything to suggest that 

 the ribs in fishes are homologous with tl^eprocesses which form the 

 haemal arch (h. a.) ? ^fcl 



3. Dorsal vertebrae, in the thoracic region and bearing well- 

 developed ribs which may unite with a ventral bone, the 

 sternum. 



4. Lumbar vertebrae, following the dorsal vertebrae and not 

 bearing ribs. 



5. Sacral vertebrae, usually a small number of vertebrae, fre- 

 quently fused into one piece with which the girdles of the 

 posterior appendages unite. 



6. Caudal vertebrae, posterior to the sacrum and possessing 

 no ribs. 



