CIRCULATION OF THE BLOOD. 41 



The Size of the Heart. A person's heart is about the 

 size of his clenched hand. 



The External Features of the Heart. The heart is 

 cone-shaped and the bulk of it is made up of the ventricles, 

 the auricles being two ear-like flaps at the base, one on 

 each side. There is a deep notch between the auricles 

 and the ventricles. The line of division between the two 

 ventricles is marked by a groove, which runs obliquely 

 along the ventral surface. In this groove are blood tubes 

 and usually considerable fat. 



Fig. 14B. The Heart, from behind. 



The Internal Structure of the Heart. The two halves 

 of the heart are completely separated from one another 

 by a partition. Each half, in turn, has valves which, 

 part of the time, separate the cavity of each auricle (at 

 the base) from the cavity of the corresponding ventricle 

 (at the apex). 



