176 REPTILIA. 



they continue to live and to exhibit voluntary motions, long after 

 losing their brain, and even after the loss of their head. A commu- 

 nication with the nervous system is also much less necessary to the 

 contraction of their fibres, and their muscles preserve their irrita- 

 bility after being severed from the body much longer than those of 

 the preceding classes; their heart continues to pulsate for hours 

 after it has been torn away, nor does its loss prevent the body from 

 moving for a long time. 



Thesmallness of the pulmonary vessels permits Reptiles to suspend 

 the process of respiration without arresting the course of the blood; 

 thus they dive with more facility, and remain longer under water 

 than either the Mammalia or Birds. 



No Reptile hatches its eggs. The young Batrachians, on quitting 

 the egg, have the form and branchiae of Fishes, and some of the 

 genera preserve these organs, even after the development of their 

 lungs. 



The quantity of respiration in Reptiles is not fixed like that of 

 the Mammalia and Birds, but varies with the proportion of the 

 diameter of the pulmonary artery compared to that of the aorta. 

 Thus Tortoises and Lizards respire more than Frogs, &c.; and 

 hence a much greater difference of sensibility and energy than can 

 exist between one of the Mammalia and another, or between Birds. 



The comparison, however, of their quantity of respiration and of 

 their organs of motion, has enabled M. Brogniart to divide them 

 into four orders, viz. 



The Chelonia^ or Tortoises, whose heart has two auricles, and 

 whose body, supported by four feet, is enveloped by two plates or 

 bucklers formed by the ribs and sternum. 



The Sauria, or Lizards^ whose heart has two auricles, and whose 

 body, supported by four or two feet, is covered with scales. 



The Ophidia, or Serpents^ whose heart has two auricles, and 

 whose body always remains deprived of feet. 



The Batrachia, whose heart has but one auricle, and whose body 

 is naked, most of which pass, with age, from the form of a Fish re- 

 spiring by branchiae, to that of a Quadruped breathing by lungs. 

 Some of them, however, always retain their branchiae, and a few 

 have never more than two feet. 



