THE CIRCULATOHY SYSTEM 



111 



A horse of ordinary size has a h(>art of 7 to 8 pounds in weight. 

 The pericanliuin is the filjrous sac hned with a serous membrane 

 that surrounds the heart. In it is found a characteristic secretion, 

 the pericardial jhiid. 



The internal structure of the heart is a. nic'cly arranged pumping 

 mechanism whit'h propels t lie 1 iloo( 1 always in one direction. When 



^h/ Jlur,^j 



I'lihiioiifiry jLIt-"^- 



Posltnor vena cava 

 Ltjt nfriiun 



Fig. 



-BuHc of heart, with large vessels. Photograph of specimen liardened 

 in situ. (Sisson, Anatomy of Domestic Animals.) 



the heart is opened bjr an incision for inspection it is seen to present 

 four cavities — the right and left auricles and the right and left 

 ventricles (Fig. 38). The two cavities of one side are partitioned 

 off from those of the other by a septum of fibromuscular composi- 

 tion that keeps the pure and impure blood .separated. The right 

 anterior part of the base of the licart is formed by the right auricle. 



