274 



THE VITAL FUNCTIONS. 



357 H 



shown in the diagram, Fig. 357. The heart of 

 the Frog, for example, may be considered as 

 consisting of a single ven- 

 tricle (e), and a single au- 

 ricle (d).* From the former 

 there proceeds one great ar- 

 terial trunk, which is pro- 

 perly the aorta. This aorta 

 soon divides into two trunks, 

 which, after sending branches 

 to the head and neck, bend 

 downwards (as is seen at 

 o, p), and unite to form a 

 single trunk (a), which is 

 the descending aorta. From this vessel pro- 

 ceed all the arteries which are distributed to 

 the trunk and to the limbs, and which are 

 represented as situated at b : these arterial rami- 

 fications are continued into the great venous », 

 trunks, which, as usual, constitute the vense 

 cavae (c), and terminate in the auricle (o). 



From each of the trunks which arise from the 

 primary division of the aorta, there proceed the 



* Dr. Davy has observed that although the auricle appears 

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

 into two compartments by a transparent membx^gi^s 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, 



I 



