OP VERTEBRATE ANIMALS. 67 



They live without eating for months and even years, and sur- 

 vive decapitation several weeks. 



The sauria or lizards, crocodiles, &c., have hearts resembling 

 that of the tortoise; the ribs are moveable for the purpose of 

 respiration and the lungs greatly extended. The eggs have an 

 envelope more or less hard. They have teeth, nails and scales. 

 The penis is either simple or double. 



The ophidia have a heart with two auricles, and no feet. 

 Some of them are venomous. Those which are the most so 

 have insulated fangs and a peculiar disposition of the jaw. 

 Their superior maxillary bones are very small, placed on a 

 long moveable pedicle, analogous to the external pterygoid 

 apophysis; in this is a tooth pierced by a little opening, through 

 which is ejected the poisonous fluid that is secreted by a con- 

 siderable gland seated under the eye. This tooth, together 

 with several reproductive germs of the same, being placed on 

 the maxilla, is hidden by the moveability of the latter, (when 

 the reptile does not wish to use it) in a fold of the gum. 



The batrachians or frogs, toads and salamanders have a heart 

 with but one auricle, and one ventricle. They have lungs, and 

 while young, branchiae similar to those of fishes. In this first 

 state, the circulation is like that of fishes; the artery is divided 

 and distributed in the branchiae; the vessels there unite in an 

 aortic trunk which supplies the body and even the lungs. 

 When the branchiae disappear their arteries are obliterated, 

 with the exception of two branches which unite to form the 

 aorta, and each of which send a small ramification to the lungs. 

 The eggs are membranous, and are fecundated during the time 

 of their being laid or afterwards. At its birth the young one 

 has branchiae and no feet; the first disappear as it advances in 

 age, and the feet are developed. Some preserve their branchiae 

 for life. 



60. Birds are evidently organized for flight; their figure, 

 the proportion of their parts, their great powers of respiration, 

 whence result their specific lightness and great muscular force, 

 are all combined for this mode of motion. They are biped, 

 their anterior members being solely destined for flight. The 

 chest and abdomen form one single and great cavity, whose 





