1 COMPARATIVE ANATOMY 



Amphibia. The vertebral column of Urodeles may be differ- 

 entiated into cervical, tlwraco- lumbar, sacral, and caudal regions, 

 and these regions can be recognised, except in certain modified 

 forms, in all the higher Vertebrates. On account of the absence 

 -of extremities in Csecilians, the vertebral column can only be 



FIG. 31. TAIL OF Lepidosteus. 



divided into three regions cervical, thoracic, and a very short 

 caudal. In Anura, no special lumbar region can be recognised, 

 and the caudal portion is modified to form a urostyle (see pp. 41 and 

 44). The centra of the Amphibia, as well as those of the 

 Amniota, correspond to arch-centra (see p. 39). 



FIG. 32. CAUDAL END OF VERTEBRAL COLUMN OF SALMON. (From Boas' s 



Zoology. ) 



h, centrum ; h', urostyle ; n, hasmal arch ; n' hypural bone ; o", neural arch ; t, 

 , neural spine. 



The notochord of Urodele larvae, like that of most Fishes, 

 undergoes intravertebral constrictions, while intervertebrally it 

 grows thicker, and accordingly appears expanded. Thus the 

 vertebrae here also are amphiccelous. Later, intervertebral masses 

 of cartilage become developed, which, together with the bone 

 which is formed at the same time in the surrounding connective- 



