H 



than most birds and all mammals. Reptiles differ other- 

 wise from Batrachia in having scales, scutes or plates in- 

 stead of a naked skin, though to this there are a few excep- 

 tions. The skeleton is more developed and the bones are 

 stronger. 



From Birds, on the other hand, they now differ in having 

 no feathers, in not having the power of aerial locomotion, and 

 in having a far less perfect circulatory system. The heart 

 is always located in the pectoral cavity; it has two auricles 

 and one ventricle ; the latter is generally imperfectly di- 

 vided by a septum, and on this account the venous and 

 arterial blood mingles to a greater or less extent in the 

 ventricle. Only in crocodiles is the septum perfect. From 

 the heart three great arterial trunks emerge close together, 

 sometimes from a common point and more towards the 

 right side of the ventricle ; one goes to the lungs, the other 

 two unite at some distance from the heart and form the 

 great dorsal aorta. The right auricle receives the three 

 main trunk veins in a sinus venosus, the left auricle re- 

 ceives the pulmonary veins. The right side of the ventri- 

 cle receives venous, the left arterial blood. Respiration is 

 slow and irregular, and the blood is cold. 



Reptiles agree with birds in having perfect lungs at 

 birth ; an imperfect diaphragm ; a single convex occipital 

 condyle which articulates with the spinal column ; and in 

 all having internal fertilization of the eggs, which are large 

 and in most cases hatched outside of the parent's body by 

 solar incubation, or by the heat derived from decaying 

 matter in which they may have been deposited. A few are 

 ovoviviparous. 



As in Birds and Mammals, the fcetus has an allantois and 

 an amnion. The intestines and urogenital organs open into 

 a common cloaca, as in Birds and Batrachia. Turtles have 

 simple copulatory organs, in lizards and snakes they are 

 paired. As in Birds the mandible consists of several dis- 

 tinct pieces. The articular bone of the jaw plays upon a 

 quadrate bone between the skull and the mandible. Skeletal 



