1022 CLASS AMPHIBIA. 



Posteriorly to this thoracic buckler an armour of dermal scutes is 

 generally developed on the ventral surface of the body; and in some 

 cases this armour may cover the entire body, the form of the scutes, 

 or scales, then varying considerably in the different regions. Four 

 paired pentedactylate limbs were usually present. 



The pterygoids are always separated from one another in the 

 median line. The pelvis 1 of the more typical forms is remarkably 

 like that of the Pariasaurian Anomodont Reptiles, presenting the 

 same absence of an obturator foramen. 



The paired supraoccipital ossifications constitute a feature found 

 elsewhere only among the Ganoid Fishes ; and the frequent ossifi- 

 cation of the articular bone of the mandible is also a character not 

 found elsewhere in the class. In many cases the external surface 

 of the bones of the skull (fig. 952), and of the thoracic buckler, is 



Fig. 952. — Lateral view of the imperfect left ramus of the mandible of Pachygonia incuruata ; 

 from the Lower Mesozoic of India. The letters indicate mucous canals. (After Huxley.) 



sculptured by a series of irregular grooves and ridges ; traversed in 

 the former instance by a number of mucous canals. From the 

 occurrence of a similar sculpture in the Pariasaurian Anomo- 

 donts and the Crocodilians, Professor Seeley regards these groups 

 as directly descended from Labyrinthodonts ; and it is evident that 

 the passage from the Labyrinthodonts to the former group of Rep- 

 tiles is almost a complete one. The gills (fig. 953) of the young 

 are generally lost in the adult ; but in one group the external gills 

 persist. 



Labyrinthodonts range in Europe generally from the Carboniferous 

 to the Trias, and are especially abundant in the Permian ; but one 

 genus (Rhinosaurus) persisted to the Lower Jurassic. In North 

 America and India this order is abundantly represented in strata 

 mainly representing the period from the Carboniferous to the Trias. 

 According to the views of Professor Cope and Dr Fritsch, this order 

 is to be regarded as one presenting generalised characters, some of 

 which approximate to those of modern Amphibia, while others are 



1 It should be observed that in the figure of the pelvis of Eryops given in 

 Zittel's ' Palaeontologie, ' abth. i., vol. iii., pt. ii., p. 364, fig. 351, the hinder end 

 of the ischium is mistaken for the pubis. 



