134 



THE COMMON FROG. 



[chap. 



The aortic bulb is constitutionally divided by a 

 movable septum (Fig. 79, s) in such a way, that the 

 passage on the right side of it leads to the carotid 

 and systematic arterial trunks, while the passage on 



Fig. 78. — Section of Hea't ; a and b, opei'ings of the am Ides into the ventricle ; 

 c, opening of the aortic bulb into the ventricle. 



the left side of it leads to the third pair of trunks — 

 namely, those ending in the pulmonary and cutaneous 

 arteries ; moreover, there is a valve in the first of 

 these two passages which tends to retard the flow of 

 blood [y). 



The consequence of these arrangements are as 

 follows : 



When the auricles contract, the venous blood from 

 the right auricle {RA) is sent into both right and left 

 passages of the bulb, but by the action of the valve 

 {v), and by the structure of the carotid gland, the 



