THE EEPTILIA. 



69 



The fore-limb of Reptiles never takes the form of a wing, 

 such as is seen in Birds ; the " wing " of the remarkable extinct 



Fig. 35. The occipital condyle of a Crocodile's skull viewed from behind. B.O, Basi- 

 occipital ; E.O, Ex-occipi'.al ; S.O, Supra-occipital. 



Fig. 36. 



I'a - 



Fr 



Fig. 36. The skull of a Lizard (Cyclodiis). D D, Dentaiy piece of the lower jaw : 

 Ar. Articular piece ; Qu. Os quadratum ; Sq. Fquamosal. 



flying reptiles, the Pterodactyles, being constructed on a totally 

 different principle from that of a bird. In no known reptile are 

 the metatarsal and tarsal bones ankylosed into one bone, except, 

 perhaps, in the extinct genus Compsognafhus. 



In all Reptilia the greater and lesser circulations are directly 

 connected together, within, or in the immediate neighbourhood 

 of, the heart ; so that the aorta, which is formed by the union 

 of two arches, contains a mixture of venous and arterial blood. 



