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, Raniclens ; B. Amblystoma ; 

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

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

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

 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, and the compressed transverse 

 processes are correspondingly divided. The sacral ribs of Urodeles 

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

 arches. 



