SKELETONS OF PRIMEVAL SALAMANDERS. 



Protriton, A, and Pelosaurus, B. (From Credner ; much enlarged.) 



CHAPTEE III. 

 THE PRIMEVAL SALAMANDERS, Order LABYRINTHODONTIA. 



THE remaining amphibians are extinct, and form an order mainly characteristic 

 of the upper Palaeozoic and Triassic periods, but also lingering on into the 

 Jurassic. They derive their name of Labyrinthodonts from the complex structure 

 of the teeth of the higher forms ; these displaying a peculiar pattern, caused by 

 infoldings of the outer layer, which penetrate nearly to the centre of the crown 

 in festooned lines. Most of these creatures have the general form of a salamander, 

 with the front-limbs shorter than the hinder-pair ; the latter having always five 

 toes, although in the former the number may be reduced to two. Their most 

 characteristic feature is, however, to be found in the structure of the skull, in 

 which the bones are generally covered with a pitted or radiated sculpture, 

 somewhat similar to that of crocodiles. From the accompanying figure of the 

 skull of the mastodonsaur, it will be seen that the whole of the upper surface 

 behind the sockets of the eyes is covered by a complete bony roof, extending 

 continuously from the bone marked P, which immediately covers the brain-cavity 

 to the sides of the hinder-part of the jaws (QJ), whereas in all the modern 

 salamanders this region is more or less open. This roofed skull of the 

 primeval salamanders presents an approximation to the earlier fishes; and a 

 resemblance to that group is also shown by the paired supraoccipital bones (So), 



