LABYRINTHODONTIA. 



353 



In the Permian Rocks, a few remains of LabyrinthodontS 

 have been discovered, the genus Zygosaurus being peculiar to 

 this period. 



Fig. 311. Baphetes planiceps, from the Carboniferous Rocks of Nova Scotia. (After 

 Dawson.) a Anterior part of the skull, viewed from beneath, and much reduced ; b One 

 of the largest teeth, natural size. 



In the Triassic Rocks the remains of LabyrinthodontS 

 are abundant, the most important genus being Labyrinthodon 

 or Mastodonsaurus. This genus is known mainly by foot- 

 prints and by crania ; and the size attained by some species 

 must have been colossal. No remains of this order have 

 hitherto been discovered in rocks younger than the Trias. 



CHAPTER XXXII. 

 REPTILIA. 



THE true Reptiles and the Birds, unlike as they are in external 

 appearance, are nevertheless related to one another by various 

 points of affinity ; so that they may well be included in a 

 single division, which has been termed Sauropsida by Huxley. 

 The Sauropsida are defined by the possession of the following 

 characters : At no period of existence are branchice, or water- 

 breathing respiratory organs, developed upon the visceral arches ; 

 the red corpuscles of the blood are nucleated ; the skull articulates 

 with the vertebral column by means of a single articulating surface 

 or condyle ; and each half or " ramus " of the lower jaw is com- 

 posed of several pieces, and articulates with the skull, not directly, 

 but by the intervention of a peculiar bone, called the " quadrate 

 bone" or " os quadratum " (fig. 312). 



z 



