Circulation of the Blood. 



The line of division between the two ventricles is marked 

 by a groove, which runs obliquely along the front surface. 

 In this groove are blood tubes and usually some fat. (See 

 Figs. 29 and 30.) 



, The Internal Structure of the Heart. The two halves 

 of the heart are completely separated from one another by 

 a partition. Each half has valves which, part of the time, 

 separate the cavity of each auricle (at the base) from the 

 cavity of the ventricle (at the apex). 



Pre caval Vein 



Right Pulmonary Artery 



Right Pulmonary Veins 



Post-caval Vein 



Right Auricle 



Fig. 30. The Heart, from behind. 



The Valves of the Heart. Between the auricles and the 

 ventricles are curtain-like valves (see Fig. 33), whose 

 upper edges are attached to the inner surface of the walls 

 at the upper margin of the ventricle. These flaps are 

 somewhat triangular, and have strong, white, tendinous 

 cords extending from their edges and under surfaces to 

 the walls of the ventricle below. In the right half of the 

 heart there are three flaps, and this valve is called the 

 tricuspid valve. In the left side there are two flaps, which, 

 together, make up the mitral valve. In the resting heart 



