VERTEBRAL COLUMN. 



41 



different stages of development find a complete parallel in the 

 phylogeny of tailed Amphibians, inasmuch as all fossil forms, e.g. 

 the Stegocephala of the Carboniferous Period and the Labyrintho- 

 donts, as well as the Perennibranchiata, Derotremata, and many 

 Salamanders, possess simple biconcave vertebras, without differen- 

 tiation into definite articulations. 



The bony parts of the vertebrae of Urodeles are not formed from 

 the cartilaginous sheath of the notochord, but in the surrounding 

 connective-tissue, there being only an intervertebral cartilaginous 



FIG. 32. VERTEBRAL COLUMN OF Discoglossus pictus. 



Pa, articular processes ; Ps, spinous processes ; Pt, transverse processes of trunk 

 vertebra ; Ptc, transverse processes of caudal vertebrae (urostyle, Oc] ; S W, 

 sacral vertebra ; Ob, upper arch of first vertebra ; Sg, its lateral articular 

 . surfaces ; Po, its anterior process ; E, ribs. 



zone, extending into the ends of the centra. In the Anura, on the 

 other hand, as well as in Elasmobranchs, bony Ganoids, and the 

 higher Vertebrata, the vertebrae are preformed in cartilage. 

 In the Amira true articulations are always formed between the 

 Vertebras, and, as a rule, the convexity is posterior, and the concavity / 

 anterioT~(proccelous). A further difference is seen in the rela- /ty 

 lions of the notoQho_rd,_which persists vertebrally longer than 

 intervertobrally, a condition which leads towards the Reptiles. 

 The configuration of the caudal region of the vertebral column must 



