108 TREATMENT OF DISEASES 



(membrane included) ua^yw^i tricusjns. The lateral contractions of 

 this ventricle are aided by small tendinous cords having muscular 

 origins from the wall and septum. The venous blood passes from 

 this cavity into the pulmonary tissues for oxygenation, through the 

 pulmonary artery, which emerges from the superior part of the ven-J^ 

 f.ricle. At the commencement of the pulmonary artery are found three 

 valves termed semi-lunar / their function is to guard against a retro- 

 grade movement of the blood, so that it has no other channel than 

 this which leads to the lungs. 



The left auricle has scarcely any anatomical or structural differ- 

 ences from those observed in the right, although its cavity is smaller, 

 and its walls are somewhat thicker than those found on the right. 

 It receives the blood from the lungs, after puritication, by means of 

 the pulmonary veins, which have four openings into this cavity, two 

 proceeding from the right, and two from the left lobes. The left, or 

 arterial ventricle, is the reservoir for arterial blood, which is des- 

 tined to reanimate, replenish, and perpetuate the vital economy; hav- 

 ing a vastly more important function to perform (which requires aug- 

 mented muscular mechanism,) than its duplicate found on the right 

 side, the thickness of its walls must, therefore, necessarily exceed 

 those of the right ; this is found to be the case, so that the outer 

 wall of this cavity is about three times as thick as that found on the 

 other side, and this guide is useful to us in determining, at sight, 

 after the heart is detached from the body, which is the left ventricle 

 and vice versa. 



The channel of communication between the left auricle and ven- 

 trieleis named, as is the case on the opposite side, auriculo-ventricu- 

 lar opening ; it is furnished however with only iioo, instead of three, 

 valvular openings, termed valvula bicuspis or mitralis. 



This ventricle is one of importance for our consideration, from the 

 fact that the great aorta — the plastic hose, which seldom, if ever, 

 requires cohhling or repair, here originates. Its margin or outlet is 

 guarded by a complete set of valves, three in number, termed sem^-^w- 

 nar, similar to those found at the origin of the pulmonary artery. 

 This ventricle is divided from the one on the opposite side by a mus- 

 cular and tendinous partition, termed septum ventricular um. 



Form, situation, and attachment of the heart. — Its form des- 

 cribes that simulating a cone, having a body, base and apex / its 

 base being in a superior direction, it follows, as a matter of course, 

 that its apex has an inferior insertion downwards and backwards. 



Situation. — The heart lies -in the region occupied by the fourth, 

 fifth and sixth dorsal vertebroe, right in the central region known as 

 the cavity of the chest; its apex is inclined to the left side. 



Attachment. — The base of the heart is attached to the anterior 

 and superior portion of the cavity of the chest, by the venous and 

 jirterial trunks running to and from it, and these in turn have their im- 

 inediate and intermediate unions with various tissues in the vicinity, 

 "Which tend to keep the heart in its proper position and allow of some 

 degree of motion. Above the roots of the large blood-vessels, and 

 adhering to the pleura, commences the pe7'icardium, a strong mem- 

 branous sac, which contains the heart; this sac is attached to the 

 sternum, and to a part of the tendinous portion of the diaphragm. 



Pericardium. — This tunic, called by butchers the heart-bag^ is. 



