DISEASES OF THE HEART, BLOOD VESSELS, AND 



LYMPHATICS. 



By W. H. Harbaugh, V. S. 

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



THE CIRCULATORY SYSTEM. 



In cattle, as in human beings, the heart, blood vessels, and lym- 

 phatics may be described as the circulatory apparatus. 



The heart is in the thoracic cavitj^ (chest). It is conical in form, 

 with the base or large part uppermost, ^vhile the apex, or point, 

 rests just above the sternum (breastbone). It is situated betveeen 

 the right and left lungs, the apex inclining to the left, and owing 

 to this the heart beats are best felt on the left side of the chest, behind 

 the elbow. The heart may be considered as a hollow muscle, contain- 

 ing four compartments, two on each side. The upper compartments 

 are called auricles and the lower ones ventricles. The right auricle 

 and ventricle are completelj' separated from the left auricle and 

 ventricle by a thick septum or wall, so that there is no communication 

 between the right and left sides of the organ. 



At the bottom of each auricle is the auriculo-ventricular opening, 

 each provided with a valve to close it when the heart contracts to 

 force the blood into the arteries. In the interval between the con- 

 tractions these valves hang down into the ventricles. 



The muscular tissue of the heart belongs to that class known as 

 involuntary, because its action is not controlled by the will. 



The cavities of the heart are lined by serous membrane, called the 

 endocardium, which may be considered as a continuation of the veins 

 and the arteries, forming their internal lining. The walls of the 

 ventricles ai-e thicker than those of the auricles, and the walls of the 

 left ventricle are much thicker than those of the right. 



The heart is enveloped by a fibrous sac (or bag), called the pericar- 

 dium, which assumes much of the general shape of the outer surface 

 of the heart. 



The action of the heart is similar to that of a pump and its function 

 is to keep the blood in circulation. The auricles may be considered as 

 the reservoirs or receivers of the blood and the ventricles as the pump 

 chambers. During the interval between contractions, the heart being 

 in momentary repose, the blood pours into the auricles from the 



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