290 



ZOOLOGY 



SECT. 



great diversity in the structure of the vertebral column. There 

 may be well-developed dice-box-shaped centra, or the neural arches 

 may be simply perched upon a persistent notochord surrounded by 

 incomplete hoops of bone, twice as numerous as the arches, and 

 alternately dorsal and ventral in position : the former represent 

 centra, the latter intercentra, or ossifications alternating with the 

 centra on the ventral region of the notochord. 



FIG. 957. Longitudinal sections of vertebral centra of A, Ranidens ; B. Amblystoma ; 

 C, Spelerpes ; and D, Salamandrina.- Ch. notochord ; CK, intra-vertebral cartilage 

 and fat-cells ; Ok, convex anterior face of centrum ; Gp. concave posterior face ; Jrl,. inter- 

 vertebral cartilage ; K, superficial bone of centrum ; Ligt. inter-vertebral ligament ; M h, 

 marrow-cavity ; R, transverse process ; S, intra-vertebral constriction. (From Wieders- 

 heim's Comparative Anatomy.) 



The first or cervical vertebra bears paired articular surfaces for 

 the condyles of the skull, and between them the anterior face of 

 the centrum gives off, in Urodela, a projection called the odontoid 

 process. The Urodela, moreover, have ribs articulating with the 

 transverse processes of the abdominal and sacral vertebrae : they 

 are short bones, forked proximally, andjthe compressed transverse 

 processes are correspondingly divided. The sacral ribs of Urodeles 

 give attachment to the ilia, and the caudal vertebrae bear haemal 

 arches. 



