312 



THE HEART. 



on the pulmonary artery. It is more curved than that of the right auricle, 

 and its margins are more deeply indented, 



The interior of the appendix presents musculi pectinati somewhat similar 

 to those in the right side of the heart, but the walls of the sinus venosus 

 are altogether smooth, and are also thicker than those of the right auricle. 

 Posteriorly are the openings of the pulmonary veins, usually two on each 

 side, and entirely without valves. The two veins of either or both sides 

 sometimes unite into one before entering the auricle, whilst in other cases 

 there is found an additional opening, most frequently on the right side. In 

 the lower and fore part of the auricle is situated the left auricula-ventricular 

 orifice. It is of an oval form, and is rather smaller than the corresponding 

 opening between the right auricle and ventricle. On the septum between 

 the auricles, a slight lunated mark or depression may be observed, which is 

 the vestige of the foramen ovale, as it appears on the left side. The 

 depression is limited by a slight crescentic ridge, the concavity of which is 

 turned upwards, and which is in fact the now adherent border of a mem- 

 branous valve, which during foetal life is applied to the left side of the then 

 open foramen ovale. 



4. The LEFT or POSTERIOR VENTRICLE occupies the left border of the heart, 

 but only about a third of its extent appears on the anterior surface of the 

 organ, the rest being seen behind. It is longer and narrower than the right 

 ventricle, forming by itself the apex of the heart, as the right ventricle does 

 not reach into that part. The cross section of its cavity is oval, not crescentic, 

 the septum on this side being concave. Its walla, which, excepting near the 



Fig. 23 i. Fig. 234. CKOSS SECTION OF 



THE VENTRICULAR PAKT OF 

 THE HEART AT TWO-THIRDS 

 FROM THE APEX, LOOKING 

 INTO THE CAVITIES TOWARDS 

 THE APEX. I 



1, 1', cut surface of the wall of 

 the right ventricle; 2, 2', the 

 same of the left ; 3, 3', the same 

 of the septum ; 4, the principal 

 columna carnea of the right ven- 

 tricle on its right border ; 4', 

 some of those on the septum near 

 the front ; 4", some of those on 

 the posterior wall near the sep- 

 tum ; 5, the principal anterior 

 columna carnea of the left ven- 

 tricle ; 5', the largest of those 

 situated posteriorly in the left 



ventricle ; 6, the deepest part of the cavity of the right ventricle ; 7, that of the left 



ventricle at the apex of the heart. 



apex, are three times as thick as those of the right ventricle, are thickest at 

 the part where the ventricle is widest, about one fourth of its length from the 

 base ; from this point they become thinner towards the auricular opening, 

 but they are still thinner towards the apex which is the weakest part. The 

 lining membrane, which is continuous with that of the left auricle and the 

 aorta, is usually less transparent than that of the right ventricle, especially 

 in later life. In the interior of the cavity are noticed column se carneze, 

 musculi papillares with chordae tendineae, and two orifices guarded with 

 valves. The columnce carnece are, on the whole, smaller than those of the 

 right ventricle, but are more numerous and more densely reticulated. 



