THE VASCULAR SYSTEM. 



The vascular system is composed of the central forcing 

 muscular organ, the heart ; a system of vessels, the arteries, 

 carrying the blood from the ventricles to the lungs and all 

 parts of the body; a system of vessels, the veins, returning 

 the blood to the auricles ; and numerous microscopic vessels, 

 the capillaries, connecting the termination of the arteries 

 with the origin of the veins. 



THE HEART. 



The location of the heart in the cat may be seen by re- 

 moving the ventral thoracic wall, but for the study of the 

 parts, the heart of an ox or a sheep will be found more 

 satisfactory. The heart of the cat lies between the lungs 

 (Fig. 82) in the thoracic cavity a little to the left of the 

 median line. The caudal end is the apex, and the cranial 

 end is the base. The entire organ is invested by a tough 

 membrane, the pericardium, which when cut permits the 

 pericardial fluid to run out. All the blood-vessels originate 

 from the dorsocranial aspect of the heart. 



It is composed of a right and left half, each of which 

 consists of an auricle and a ventricle. The separation be- 

 tween the two halves is apparent on the ventral surface. 

 The auricles receive the blood from the veins and pass it 

 to the ventricles, which disperse it through the arteries. 

 There is no aperture between the auricles or the ventricles. 

 The aperture between the right auricle and the right ven- 

 tricle is guarded by the tricuspid valve which prevents the 

 blood from returning into the auricle when the systole or 

 contraction pushes the blood into the pulmonary artery. 



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