CIRCULATION IN UEPTILES. 



247 



353 ^^ 



actions of the body in the former than in the latter, 

 and the necessity of a heart appropriated to that 

 office is, consequently, in a great measure super- 

 seded.* 



The circulation in Reptiles is not double, like 

 that of fishes; for only a part of the blood is 

 brought under the influence of the air in the pul- 

 monary organs. The analysis of this mode of 



circulation may be understood 

 from the diagram. Fig. 353 : in 

 which it will be seen that the 

 pulmonary is only a part of the 

 general or systemic circulation. 

 All the animals belonging to 

 this class are cold-blooded, slug- 

 gish, and inert; they subsist 

 upon a scanty allowance of 

 food, and are astonishingly te- 

 nacious of life. The simplest 

 form in which we meet with 

 this mode of circulation is in 

 the Batrachia ; it is shown more correctly in Fig. 

 357, than in the analytical diagram. The heart of 

 the Frog may be considered as consisting of a 

 single auricle (u), and a single ventricle (e).! 

 From the latter there proceeds one great arterial 



* See Owen, Trans. Zool. Soc. vii, 218. 



f Dr. Davy has observed that ahhough the auricle appears 

 single, when viewed externally, its cavity is in reality divided into 

 two compartments by a transparent membranous partition, in which 

 some muscular fibres are apparent : these communicate with the 

 cavity of the ventricle by a common opening, provided with three 

 semilunar valves. Edin. Phil. Journal; xix, 161. 



Mr. Owen informs me that his own observations confirm those of 



