THE HEART. 463 



most distinct above and at the sides; below, it is deficient. A small slit-like 

 valvular opening is occasionally found, at the upper margin of the fossa ovalis, 

 which leads upward beneath the annulus into the left auricle, and is the remains 

 of the aperture between the two auricles in the fetus. 



The tnlx'rrultini Loircri is a small projection on the right wall of the auricle, 

 between the two venae cavae. It is most distinct in the hearts of quadrupeds ; in 

 man it is scarcely visible. It was supposed by Lower to direct the blood from the 

 superior cava toward the auriculo-ventricular opening. 



The Right Ventricle is triangular in form, and extends from the right auricle to 

 near the apex of the heart. Its anterior or upper surface is rounded and convex, 

 and forms the larger part of the front of the heart. Its under surface is flattened, 

 rests upon the Diaphragm, and forms only a small part of the back of the heart. 

 Its posterior wall is formed by the partition between the two ventricles, the septum 

 ventriculorum, so that a transverse section of the cavity presents a semilunar outline. 

 The surface of the septum is convex and bulges into the cavity of the right ventricle. 

 Its upper and inner angle is prolonged into a conical pouch, the infundibulum, or 

 conns 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 3. The wall is thickest at the base, and gradually becomes thinner toward 

 the apex. The cavity equals in size that of the left ventricle, and is capable of 

 containing about three fluidounces. 1 



To examine the interior of the right ventricle, its anterior wall should be turned downward 

 and to the right in the form of a triangular flap. This is accomplished by making two incisions : 

 (1) from the pulmonary artery to the apex of the ventricle parallel to, but a little to the right 

 of, the anterior interventricular furrow; (2) another, starting from the upper extremity of the 

 first and carried outward parallel to, but a little below, the auriculo-ventricular furrow, care 

 being taken not to injure the auriculo-ventricular valve. 



The following parts present themselves for examination : 



^ f Auriculo-ventricular. 



" S \ Opening of the pulmonary artery. 



Valves fTricuspid. 

 ( bemiluriar. 



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

 Columnae carnese. Chordae, tendineae. 



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. It is about an inch and a half in diameter, 2 oval 

 from side to side, surrounded by a fibrous ring, covered by the lining membrane of 

 the heart; it is considerably larger than the corresponding aperture on the left side, 

 being sufficient to admit the ends of four fingers. It is guarded by the tricuspid valve. 



The openin;/ <>f fhc pulmonary artery is circular in form, and situated at the 

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

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

 aspect of the heart. Its orifice is guarded by the pulmonary 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, which contains, according to Kiirschner and Senac, 



1 Morrant Baker says that "taking the mean of various estimates, it may be inferred that each 

 ventricle is able to contain four to six ounces of blood" (Kirke's Physiology, 10th edition, p. 15(5). 



2 In the Pathological Transactions, vol. vi., p. 119, Dr. Peacock has given some careful researches 

 upon the weight and dimensions of the heart in health and disease. He states, as the result of his 

 investigations, that, in the healthy adult heart, the right auriculo-ventricular aperture has a mean 

 circumference of 54.4 lines, or 4|^ inches; the left auriculo-ventricular aperture a mean circumfer- 

 ence of 44.3 lines, or 3|| inches; the pulmonic orifice of 40 lines, or 3Jf inches; and the aortic orifice 

 of 35.5 lines, or 3,/j- inches; but the dimensions of the orifices varied greatly in different cases, the 

 right auriculo-ventricular aperture having a range of from 40 to 50 lines, and the others in the same 

 proportion. 



