GENERAL CHARACTERS 



ii 



the two parietal bones which communicates with that region 

 of the brain known as the epiphysis. It is also present in the 

 primeval salamanders ; and in the tuatera overlies the remnants 

 of an aborted and degenerate eye. From a certain want of 

 symmetry in this structure in the tuatera it has been inferred 



Fig. i, — A, Upper surface of skull of a Labyrinthodont Amphibian to show the 

 roofed type. B, Upper surface of skull of Tuatera (Sphenodon) to show open type. 

 C, Front view of the lower end of the tibia of a bipedal Dinosaur with the closely- 

 applied astragalus. The hole in Pt. is the parietal foramen. 



that the parietal eye was originally double ; and that ancestral 

 vertebrates were furnished with a pair of such eyes, which may 

 have been serially homologous with the single pair of their 

 descendants. It should, however, be added that no creature 

 has hitherto been discovered whose skull exhibits apertures 

 for this hypothetical second pair of eyes. 



In regard to limbs, it would appear that reptiles were 

 originally four-footed creatures, with five toes to each foot. In 



