s 
SKELETONS OF PRIMEVAL SALAMANDERS. 
Protriton, A, and Pclosaurus, B. (From Credner; much enlarged.) 
CHAPTER 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), 
