VERTEBRA AND RIBS 



39 



larger, dividing, with growth in the same way as in Lepidosteus 

 resulting in a ball and socket joint (opisthocoelous, fig. 43, //, i). 

 A few Salamandrina are amphicoelous. 



The Urodeles have low spinous processes and the trunk vertebras 

 have diapophyses. The haemal arches in the tail are usually well 

 formed, at least anteriorly. The first vertebra (atlas) has its cen- 

 trum greatly reduced, and on either side has a cup-shaped depression 

 for the occipital condyle of the skull. 



Fig. 44. — Vertebra of adult Cryptobranchus japonicus (Hoffmann, '74). 

 brarterial canal; 5, spinal canal; z, zygapophysis. 



a, verte- 



The Urodele rib has apparently been misunderstood. The rela- 

 tions in the tail are normal (fig. 22, A) except that the rib, between 

 ep- and hypaxial muscles, is continuous with the centrum. In the 

 trunk of a three months larva of Cryptobranchus (fig. 45, ^) the same 

 parts are recognizable, but later, as in Triton, the part representing 



Fig. 45. — A, Vertebra of Cryptobranchus allegheniensis 3 months after hatching; B, 

 Triton 35 mm. long, right and left sides from different sections, a, vertebral artery; 

 d + t, diapophysis and tubercular head; p, parapophysis; p + c, parapophysis and 

 tubercular head; r, rib; s, secondary connexion of rib and neural arch. 



diapophysis and tubercular head, has been perforated (fig. 45, B) so 

 that there is a secondary connexion is) of rib and vertebra, while 

 ventrally the parapophysial-capitular connexion has largely disap- 

 peared. In some genera the rib extends farther and becomes seg- 

 mented in such a way as to appear as if the upper connexion were the 

 tubercular one and the true tubercular looks like a capitular. It is 

 clear from the earlier relations that the Amphibian rib is homologous 

 with those of Amniotes. 



