XII 



PHYLUM CHORD ATA 



333 



196) the centra have concave anterior and convex posterior 

 surfaces and the vertebne are accordingly said to be 

 proccehus. In the latter (Fig. 197), the surfaces are flat, 

 and discs of fibre-cartilage, the inter-vertebral discs, are 

 intercalated between the vertebrae. In both the spinal 



n a, 



tr.Jbr 



fa ou 



FIG. 195. A, three trunk vertebrae of Dog-fish from the side ; B, a single trunk 

 vertebra viewed from one end ; C, three caudal vertebrae from the side ; D, a 

 single caudal vertebra from one end. c. centrum ; h a. haemal arch ; n. a. neural 

 arch ; tr.pr. transverse process. (After Hasse.) 



column is divisible into five regions the cervical, the 

 tlwracic, the lumbar, the sacral and the caudal. In the 

 Rabbit the vertebrae of the cervical region are devoid 

 of ribs ; in the Lizard they have short ribs with the 

 exception of the first three. The first and second vertebrae 

 (atlas and axis) in both the Rabbit and the Lizard are 



