THE THORAX 975 



atria of the auricles and the origins of the aorta and pulmonary 

 ari:ery, the former being behind, and the latter in front. 



The surfaces are antero-superior and inferior. The antero- 

 superior surface is convex, and is traversed by the antero-superior 

 interventricular groove. As this groove lies near the left border, 

 the greater part of this surface (about two-thirds) is formed by the 

 right ventricle, and the remainder by the left ventricle. In post- 

 mortem examinations, therefore, when the pericardium is opened, 

 the right ventricle is chiefly exposed for inspection. On this 

 aspect of the right ventricle there are the anterior cardiac veins. 

 Its upper and left part is somewhat conical, and is called the in- 

 fundibiilum or conus arteriosus. It gives origin superiorly to the 

 trunk of" the pulmonary artery. The inferior surface is flat, and 

 is traversed by the inferior interventricular groove. As this groove 

 lies near the inferior border, the greater part of this surface (about 

 two-thirds) is formed by the left ventricle, and the remainder by 

 the right ventricle. On this aspect of the left ventricle there are 

 the posterior cardiac veins. 



The borders are inferior (right) and left. The inferior border is 

 comparatively long, and extends from right to left. It is formed 

 by the right ventricle, and is sharp in outline, from which circum- 

 stance it is known as the margo acutus. The marginal branch of 

 the right coronary artery and one of the anterior cardiac veins 

 lie along it. The left border is shorter than the inferior, and is 

 blunt and round, from which circumstances it is known as the 

 margo obtusiis vel rotundtts. The marginal branch of the left 

 coronary artery lies along it. 



Interior of the Heart — Right Auricle. — The wall of the auricular 

 appendix is marked by a number of muscular elevations, arranged 

 as closely-set, vertical, parallel bands, like the teeth of a comb, 

 from which circumstance they are called the musculi pectinati. 

 These bands, relatively to each other, are more or less reticular. 

 They are also present on the right wall of the atrium, being more 

 comb-like here than in the appendix, and they terminate posteriorly 

 at a vertical ridge, called the crista terminalis. This crest cor- 

 responds in position to the sulcus terminalis externally, and it has 

 the same significance. Internally and posteriorly the walls of the 

 auricular atrium are destitute of musculi pectinati, and present 

 a smooth appearance. The atrium of the right auricle presents 

 the following openings : the opening of the superior vena cava ; 

 the opening of the inferior vena cava ; the opening of the coronary 

 sinus ; the foramina Thebesii ; and the auriculo- ventricular opening. 

 The orifice of the superior vena cava, which is destitute of a 

 valve, is situated at the postero-superior angle of the atrium. It 

 is directed downwards and forwards, and the upper part of the crista 

 terminalis is continuous with its anterior margin. 



The orifice of the inferior vena cava is situated at the postero- 

 inferior angle of the atrium, and is directed upwards and inwards. 

 In front of the orifice, and to a certain extent overlapping it, there 



