SKELETON, NERVOUS SYSTEM, ETC. 215 



As in Birds, the Reptiles have the lower jaw connected 

 with the skull by means of a quadrate bone (Fig. 163) ; and, 

 'as in Birds also, the skull is connected with the first ver- 

 tebra of the neck by means of only one occipital condyle. 



The motatory apparatus of Reptiles that is, the skele- 

 ton, muscles, tendons, etc. corresponds in its plan of 

 structure to that of the higher vertebrates. The skeleton, 

 though apparently so different from that of Mammals and 

 Birds, nevertheless contains the same elements of struc- 

 ture as are found in these two classes. Compare Fig. 249 

 with Figs. 24 and 162. 



As to the nervous system of Reptiles, it may be stated 

 that the brain is small, and without convolutions, and the 

 hemispheres are hollow. In comparison to the brain the 

 spinal cord is large. 



The brain of a Sea-Tortoise \veiglis only TsVti of the entire animal. 

 In several small birds and quadrupeds, the brain exceeds -^ of the 

 weight of the body. 



Reptiles continue to live and exhibit movements long 

 after losing the brain, and even after the head is cut oil'. 

 The muscles preserve their irritability for a considerable 

 time after being severed from the body ; and even the 

 heart pulsates for hours after it is removed, nor does its 

 loss prevent the animal from moving about. 



The eyes of Reptiles resemble those of Birds. Some 

 have three eyelids ; others, as serpents, have none, and 

 hence their fixed and staring look. 



The hearing apparatus is far less complete than that of 

 Birds and Mammals. The external ear is wanting ; there 

 is no auditory canal ; the drum of the ear is on a level 

 with the surface of the head : the tympanic cavity is im- 

 perfectly formed ; the bones of the ear are in most cases 

 absent; and the cochlea is often only rudimentary. 



