THE BATEACHIA OF NORTH AMERICA. 



9 



extinct orders of Batrachia are not the centra of the higher vertebrata^ 

 but are iuterceutra, which are occasionally seen in the higher vertebrates 

 in a rudimeutal condition. This is especially the case in the remark- 

 able saurian of New Zealand, the Sphenodon, and in the extinct order 

 of the Theromora. Owen has shown that the intercentra exist also in 

 the mole. I have given the following reasons for this view : 



1. The intercentra are very large in the Ganocephala and Ehachi- 

 tomi. 



2. They support the neural arch in the Embolomeri. 



3. They are not rudimental in existing Batrachia, 



4. The chevron bones, which originate from the intercentra of Eep- 

 tilia, are continua with the caudal vertebral bodies in Batrachia. 



5. The ribs, which originate from the intercentral cartilages in Eep- 

 tilia^ originate from the vertebral bodies of Batrachia. 



The paleontology of the Batrachia and Eeptilia shows that the order 

 Embolomeri is the only one with complete vertebral bodies, and so 

 probably gave origin to the reptiles ; while the intercentra in some 

 Batrachians become so connected with the neural arches as to lead to the 

 belief that they become the vertebral bodies of later forms of the class 

 which have descended from them. 



In all the orders, genera with well-developed anterior limbs display 

 well-developed distal condyles of the humerus. They are better de- 

 veloped than in any order of reptiles, with the exception of the Thero- 

 mora. 



With regard to the cranial nerves, it is to be remarked that the latera- 

 lis branch of the vagus is present, as in fishes ; also that the glossopha- 

 ryngeal is united with the vagus. In the Urodela the uervus facialis is 

 distinct from the trigeminus (Fig. 1), but in the Salientia they are 

 united. (Plate 43.) 



r.nas. 



glph^vag. 



rZal.sup. r.intest 



T.TTUXOC^ 



riatin^ 



Fig. 1. Diagram of chondrocranium and cranial nerves of Salamandra, side view (from Wiedersheim). 



In the muscular system the Batrachia differ from the fishes in the 

 modifications which partially take the place of the myocommata, and 

 the development of the muscles of the limbs and their extension on 

 the dorsal and ventral surfaces of the body. Myocommata persist in. 



