DISEASES OF THE HEART, BLOOD VESSELS, AND 



LYMPHATICS. 



By M. R. Tkumboweb, V. S. 

 [Revised l)y I.oouard rearson, 15. S., V. M. D.] 



ANATOMY AND PHYSIOLOGY OF THE HEART AND BLOOD 



VESSELS. 



(Pis. XX and XXI.) 



The lieait 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 hoi-ses used for speed the heart is relatively larger, 

 according to the weight of the animal, than in hoi-ses used for slow 

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

 held in position 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- 

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

 adherent to the heart, tlie 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. 



Tlie heart is divided by a sliallow fissure into a right and left side; 

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

 comjiartments which conmnniicate. Thus there are four cardiac 

 cavities — the superior, or ujjper, ones called the aiuicles; 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 whicli passes thiough 

 them. The auricles are thin-walled cavities placed at tlie l)a,se, and 

 are connected with the great veins — the venie cavae and pulmonary 

 veins — through which they receive blocnl froui all jiarts of the body. 

 The auricles comuumicate with the ventricles each by a large upev- 



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