Class 3. Amphibia, 



39a 



contrary-j it is intervertebrally constricted, tlie vertebrae articu- 

 lating by joints; in tke Urodela the vertebrae are opistlioccE- 

 1 o u s (concave behind, convex in front) ; in the Anura usually 

 proccelous (convex behind, concave in front) . Just as in Pisces, 

 but in contradistinction to the classes following, the second cervical 

 vertebra is not specially modified (c/., Eeptilia). The first, with 

 which the head articulates, and the last or sacral vertebra, to which 

 the pelvis is attached, differ from all the others. The caudal verte- 

 brse of the Urodela are provided with haemal arches ; in the 

 Anura, where they are twice as numerous in the larva as in the 

 adult, they are fused into a long, unjointed bone, the urostyle* 

 (Fig. 323 C) . The ribs never reach the sternum ; in some extinct 

 Amphibia (Stegocephala) they were well-developed; in all living 

 forms they are, however, very degenerate ; they are best developed 

 in the Urodela and Gymnophiona, where they are short processes 

 usually present on all the trunk vertebrae except the first; in the 

 Urodela they occur on the anterior caudal vertebrae also. In the 

 Anura the ribs are rudimentary, and in the adult usually fused with 

 the long transverse processes. The sternum (Fig. 321-22) is not 

 connected with the ribs, but is closely attached to the lower portion of 

 the shoulder girdle ; in the Urodela it is a short cartilaginous plate, 

 with the insertion of the coracoid at its anterior edge ; in the Anura 

 it is often partially ossified, and closely connected with the coracoids. 

 The cranial skeleton is in many points very similar to that of 

 the Ganoids and Teleostei. Considerable portions of the cartilaginous 





III- 



Fig. 319. The visoeral arches of the Salamander, seen from below ; A larva, B adult. 

 c basibranohials, c' the last (separated from the others in the adnlt), Ic mandible, h hyoid 

 arch, ir 1 — 4 first to the fourth gin-bars, Z occipital condyles, o eye. After Busconi. 



* The tail is not -visible externally, for the long ilia, which are attached by their 

 anterior ends to the sacral vertebra, extend backwards almost parallel to the urostyle ; 

 the latter is of about the same length as the ilia, so that their glenoid cavities are 

 close to its tip. 



