DISEASES OF THE HEART, BLOOD VESSELS, AND 



LYMPHATICS. 



By M. E. Teitmboweb, V. S. 

 [Revised by Leonard Pearson, B. S., V. M. D.] 



ANATOMY AND PHYSIOLOGY OF THE HEART AND BLOOD 



VESSELS. 



(Pis. XX and XXI.) 



The heart is a hollow, muscular organ, situated a little to the left 

 of the center of the chest. Its impulse is felt on the left side on 

 account of its location and from the rotary movement of the organ 

 in action. It is cone-shaped, with the base upward ; the apex points 

 downward, backward, and to the left side. It extends from about 

 the third to the sixth ribs, inclusive. The average weight is about 

 7 to 8 pounds. In horses used for speed the heart is relatively larger, 

 according to the weight of the animal, than in horses used for slow 

 work. It is suspended from the spine by the large blood vessels and 

 held in positicwi below by the attachment of the pericardium to the 

 sternum. It is inclosed in a sac, the pericardium, which is com- 

 posed of a dense fibrous membrane lined by a delicate serous mem- 

 brane, which is reflected over the heart; the inner layer is firmly 

 adherent to the heart, the outer to the fibrous sac, and there is an 

 intervening space, known as the pericardial space, in which a small 

 amount of serum — a thin translucent liquid — is present constantly. 



The heart is divided by a shallow fissure into a right and left side; 

 each of these is again subdivided by a transverse partition into two 

 compartments which conununicate. Thus there are four cardiac 

 cavities — ^the superior, or upper, ones called the auricles ; the inferior, 

 or lower, ones the ventricles. These divisions are marked on the 

 outside by grooves, which contain the cardiac blood vessels, and are 

 generally filled with fat. 



The right side of the heart may be called the venous side, the left 

 the arterial side, named from the kind of blood which passes through 

 them. The auricles are thin-walled cavities placed at the base, and 

 are connected with the great veins — ^the vense cavse and pulmonary 

 veins — ^through which they receive blood from all parts of the body. 

 The auricles communicate with the ventricles each by a large aper- 



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