DISEASES OF THE HEART, BLOOD VESSELS, 

 AND LYMPHATICS. 



By M. R. Trumbowek, V. S. 



[Revised in 1903 by Leonard Pearson, B. S., V. M. D.] 



ANATOMT AND PHYSIOLOGY OF THE HEART AND BLOOD VESSELS. 



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 posi- 

 tion below by the attacliment of the pericardium to the sternum. It 

 is inclosed in a sac, the pericardium, which is composed of a dense 

 fibrous membrane lined by a delicate serous membrane, 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 communicate. 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 out- 

 side 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 venae 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- 

 ture, the auriculo-ventricular orifice, which is furnished with a 

 remarkable mechanism of valves, allowing the transmission of blood 

 from the auricles into the ventricles, but preventing a reverse course. 

 The ventricles are thick-walled cavities, forming the more massive 

 portion of the heart toward the apex. They are separated by a par- 

 tition, and are connected with the great arteries — the pulmonary 

 artery and the aorta — ^by which they send blood to all parts of the 

 H. Doc. 795, 59-2^ 15 225 



