THE HEART. 1089 



heart. Some of these foramina are minute depressions in the walls of the heart, 

 presenting a closed extremity. 



The auricula-ventricular opening is the large oval aperture of communication 

 between the auricle and the ventricle, to be presently described. 



The Eustaehian valve is situated between the anterior margin of the inferior 

 vena cava and the auriculo-ventricular orifice. It is semilunar in form, its convex 

 margin being attached to the wall of the vein ; its concave margin, which is free, 

 terminating in two cornua, of which the left is attached to the anterior edge of 

 the annulus ovalis, the right being lost on the wall of the auricle. The valve is 

 formed by a duplicature of the lining membrane of the auricle containing a few 

 muscular fibres. 



In the foetus this valve is of large size, and serves to direct the blood from the 

 inferior vena cava, through the foramen ovale, into the left auricle. 



In the adult it is occasionally persistent, and may assist in preventing the 

 reflux of blood into the inferior vena cava : more commonly it is small, and its 

 free margin presents a cribriform or filamentous appearance ; occasionally it is 

 altogether wanting. 



The coronary valve (valve of Thebesius) is a semicircular fold of the lining 

 membrane of the auricle, protecting the orifice of the coronary sinus. It prevents 

 the regurgitation of blood into the sinus during the contraction of the auricle 

 This valve is occasionally double. 



The fossa ovalis is an oval depression corresponding to the situation of the 

 foramen ovale in the foetus. It is situated at the lower part of the septum auricu- 

 larum. above and to the left of the orifice of the inferior vena cava. 



The annulus ovalis is the prominent oval margin of the foramen ovale. It is 

 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 foetus. 



The musculi pectinati are small, prominent muscular columns which run across 

 the inner surface of the appendix auriculae and adjoining portion of the wall of the 

 sinus. Posteriorly, they join a vertical ridge, the crista terminalis of His. They 

 are called pectinati from their fancied resemblance to the teeth of a comb. 



The Eight Ventricle i? 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, the surface of which is convex and bulges 

 into the cavity of the right ventricle. Its upper and left angle is prolonged 

 into a conical pouch, the infundibulum or conns arteriosus, from which the pul- 

 monary 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, which 

 equals that of the left ventricle, is capable of containing about three fluidounces. 1 



To examine the interior of the right ventricle, an incision should be made a little to the 

 right of the anterior interventricular groove from the pulmonary artery to the apex of the 

 heart, and should be carried up from thence a little to the right of the posterior interventricular 

 groove, as far as the auriculo-ventricular opening. 



The following parts present themselves for examination : 



Q f Auriculo-ventricular. 



G:> \ Opening of the pulmonary artery. 



Valves / Tricuspid. 

 ~- milunar. 



1 Morrant Baker says that '' taking the means 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. 156). 

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