234 MANUAL OF MODERN FARRIERY 



of the back, from which it is suspended in its situa- 

 tion in the middle of the cavity of the chest, by the 

 attachment of the venous and arterial trunks im- 

 mediately connected with it. Its apex hangs loose 

 within the cavity of the pericardium, pointing down- 

 wards and backwards, and rather inclined towards 

 the left side. It is composed of four cavities : the 

 two uppermost are called auricles, from their form 

 being somewhat like the ear of a dog ; and two 

 ventricles, or belly-shaped cavities, which occupy the 

 substance of the heart. Although the heart is chiefly 

 composed of fleshy fibres, still a tendinous substance 

 is found in the middle, which seems to be the common 

 medium of attachment between its auricles, ventricles, 

 and vessels, one to another. 



The heart is supplied with blood by two coronary 

 arteries ; the first branches are given off from the 

 aorta, or great artery. Its veins pour their blood 

 into the coronary vein, by which it is returned into 

 the right auricle. 



There are two orders of blood-vessels, arteries and 

 veins ; the former conduct the flood from the heart to 

 all parts of the body, nourishes it, and returns to the 

 heart through the veins. It enters the auricle on the 

 right side, where it is accumulated as a reservoir, until 

 there is sufficient to fill the ventricle below. The 

 auricle then contracts, and forces the blood into the 

 ventricle, which in its turn contracts, and drives the 

 blood through an aperture that leads to the lungs. 

 It cannot be drawn again into the auricle, because 

 there is a complete valve, like that of a sucker of a 

 pump, to prevent this. The blood which has thus 

 been forced into the lungs traverses every portion of 

 them, by the minutely ramified blood-vessels, and 

 entering all the little cells, there to undergo the 



