CHAPTER IX 



h 



M 



DISEASES OF THE CIRCULATORY ORGANS 



General Discussion, — The circulatory organs are the heart, 

 arteries, veins and lymphatics. The heart is the central organ 

 of the circulatory system (Fig. 23). Its function is to force 

 the blood through the blood-vessels. It is situated in the thoracic 

 cavity between the lungs, and enclosed by a special fold of the 



^______^ __, pleura, the pericardial 



sack. There are two 

 kinds of blood-vessels, 

 arteries and veins. 

 The arteries leave the 

 heart and carry the 

 blood to the many dif- 

 ferent organs of the 

 body. The veins re- 

 turn to the heart and 

 carry the blood from 

 the body tissues. The 

 capillaries are small 

 blood-vessels, micro- 

 scopic in size, that con- 

 nect the arteries with 

 the veins. The arte- 

 ries carry the ]iure 

 blood. The opposite is true, however, of the lesser or pul- 

 monary system. The pulmonary artery carries the impure 

 blood to the lungs, and the pulmonary veins carry the pure blood 

 back from the lungs. The Ijimpliatic vessels carry a transparent 

 or slightly colored fluid and chyle from the tissues and ali- 

 mentary canal. This system of vessels empties into the venous 

 system. 

 104 



Fig. 23. — Photograph of model of horse's heart: 

 (A) auricle; (B) ventricle; (C) pulmonary artery; 

 (F) pulmonary veins; (D) posterior aorta; and (E) 

 anterior aorta. 



