G94 THE THORAX. 



The EIGHT VENTKICLE is triangular in form, and extends from the right auricle 

 to near the apex. Its anterior or upper surface is rounded and convex, and forms 

 the larger part of the front of the heart. Its posterior or under surface is flattened, 

 rests upon the Diaphragm, and forms only a small part of this surface. Its inner 

 wall is formed by the partition between the two ventricles, the septum ventricu- 

 lorum, the surface of which is convex, and bulges into the cavity of the right 

 ventricle. Superiorly, the ventricle forms a conical prolongation, the infundi- 

 bulum or conus arteriosus, from which the pulmonary artery arises. The walls of 

 the right ventricle are thinner than those of the left, the proportion between them 

 being as 1 to 2 (Bizot). The thickest part of the wall is at the base, and it 

 gradually becomes thinner towards the apex. Its cavity, which equals that of the 

 left ventricle, is capable of containing about two fluid ounces. 



To examine its interior, an incision should be made a little to the right of the anterior ven- 

 tricular groove from the pulmonary artery to the apex of the heart, and from thence carried up 

 along the right border of the ventricle, as far as the auriculo-ventricular opening. 



The following parts present themselves for examination : 



~ . j Auriculo-ventricular. 



ings . . | Op en i n g O f tne pulmonary artery. 



-r T -i \ Tricuspid. 



Valves. . . 



And a muscular and tendinous apparatus connected with the tricuspid valves : 

 Columnar carneas. Chordae tendinese. 



The auriculo-ventricular orifice is the large oval aperture of communication 

 between the auricle and ventricle. It is situated at the base of the ventricle, near 

 the right border of the heart, and corresponds to the centre of the sternum 

 between the third costal cartilages. The opening is about an inch in diameter, 

 oval from side to side, surrounded by a fibrous ring, covered by the lining mem- 

 brane of the heart, and is rather larger than the corresponding aperture on the 

 left side, being sufficiently large to admit the ends of three fingers. It is guarded 

 by the tricuspid valve. 



The opening of the pulmonary artery is circular in form, and situated at the 

 summit of the conus arteriosus, close to the septum ventriculorurn. It is placed 

 on the left side of the auriculo-ventricular opening, upon the anterior aspect of 

 the heart, and corresponds to the upper border of the third costal cartilage of the 

 left side, close to the sternum. Its orifice is guarded by tl^e semilunar valves. 



The tricuspid valve consists of three segments of a triangular or trapezoidal 

 shape, formed by a duplicature of the lining membrane of the heart, strengthened 

 by a layer of fibrous tissue, and containing, according to Kiirschner and Senac, 

 muscular fibres. These segments are connected by their bases to the auriculo- 

 ventricular orifice, and by their sides with one another, so as to form a continuous 

 annular membrane, which is attached round the margin of the auriculo-ventricular 

 opening, their free margins and ventricular surfaces affording attachment to a num- 

 ber of delicate tendinous cords, the chordse tendinese. The largest and most mov- 

 able segment is placed towards the left side of the auriculo-ventricular opening 

 interposed between it and the pulmonary artery. Another segment corresponds 

 to the front of the ventricle ; and. a third to its posterior wall. The central part of 

 each segment is thick and strong ; and the lateral margins are thin and indented. 

 The chordae tendineas are connected with the adjacent margins of the principal 

 segments of the valve, and are further attached to each segment in the following 

 manner : 1. Three or four reach the attached margin of each segment, where they 

 are continuous with the auriculo-ventricular tendinous ring. 2. Others, four to 

 six in number, are attached to the central thickened part of each segment. 3. The 

 most numerous and finest are connected with the marginal portion of each 

 egment. 



