CHAP. XXVIII.] CAVITIES AND VALVES OF THE HEAKT. 333 



into two, by means of a groove, which corresponds to the anterior 

 and posterior margins of the septum of the ventricles, and which 

 passes from hase to apex. The anterior groove contains the left 

 coronary artery and vein : the posterior the right coronary artery and 

 vein. These are accompanied hy nerves. A transverse groove of con- 

 siderable depth separates the auricles from the ventricles ; it contains 

 the coronary vein. All the grooves contain a greater or less quantity 

 of fat, which envelopes the vessels and nerves lodged in them. 



Of the four cavities of the human heart, a ventricle and auricle 

 are on each side of the median groove. The ventricles are cone- 

 shaped cavities, their apices being directed towards the apex of the 

 heart, their bases corresponding to the auricles. The left ventricle 

 forms the apex of the heart. When the right ventricle is dilated, 

 its wall extends to, and contributes to form, the apex. Each ven- 

 tricle, when laid open, exhibits two distinct parts ; one, which com- 

 municates with the auricle by a large and free aperture, called the 

 auriculo-ventricular orifice, through which the blood passes from the 

 auricle into the ventricle ; the other, called the infundibulum, a 

 funnel-shaped channel, which leads to the artery, and through which 

 the blood is propelled into it from the cavity of the ventricle. 



The Valves of the Heart. The auriculo-ventricular orifice on 

 each side is guarded by certain valves which, when not in action, 

 lie in the ventricle. The valve of the left side consists of two 

 triangular curtains, from the free margin and part of the ventricular 

 surface of which tendinous chords (chorda tendinece) pass to various 

 points of the wall of the ventricle. The bases of these curtains are 

 attached along a fibrous zone, which separates the auricle from the 

 ventricle. This valve is known by the name of the mitral valve, 

 and the orifice is called the mitral orifice ; the larger curtain is that 

 which separates the infundibulum from the body of the ventricle. 

 The valve at the right auriculo-ventricular orifice, consists of three 

 portions, each having a pointed free extremity extending into the 

 ventricle, and connected to its wall by tendinous cords. Hence 

 this is called the tricuspid valve. The base of each segment cor- 

 responds to the fibrous zone which intervenes between the auricle 

 and ventricle. Of the three curtains, of which the tricuspid valve 

 consists, the largest is anterior, and the next in size corresponds to 

 the infundibulum of the ventricle. 



At each of the arterial orifices of the ventricles there are three 

 valves of semilunar form (Fig. 199), which effectually close the 

 rnouth of the artery against the regurgitation of blood into the ven- 

 tricle. Each of these valves has a convex border attached along the 



