THE LEFT VENTRICLE. 313 



Their intersections are very numerous near the apex of the cavity, and also 

 along its posterior wall, but the upper part of the anterior wall and septum 

 is comparatively smooth. The musculi papillarcs are collected into two 

 bundles, which are larger than those of the right ventricle, and are formed 

 one from the anterior, the other from the posterior surface of the ventricle. 

 The two orifices of this ventricle are situated very close together, with one 

 of the segments of the auriculo-ventricular valve between ; the auriculo- 

 ventricular opening being placed at the left and posterior part of the base of 

 the ventricle, behind and to the left of that which leads into the aorta. 



The bicuspid or mitral valve, which guards the auriculo-ventricular open- 

 ing, resembles in structure the tricuspid valve of the right ventricle, but it 

 is much thicker and stronger in all its parts, and consists of only two 

 pointed divisions or segments, continuous at their attached bases. The 

 larger of the two segments is suspended obliquely to the right and in front 

 of the other, between the auricular and the aortic orifices : the smaller is 

 situated to the left and posteriorly, and close to the wall of the ventricle. 

 There is usually a smaller lobe at each angle of junction of the two principal 

 segments, more apparent than those of the tricuspid valve. 



One portion of the chordae tendinese from each musculus papillaris is 

 distributed to half of one segment, and the other portion to the neighbour- 

 ing side of the other segment, so that, when the musculi papillares contract, 

 and make the segments tense, they also cause their margins to approach each 

 other. The chordae tendineas are stronger and less numerous than in the 

 right ventricle. 



The arterial or aortic orifice, circular in form, and smaller than the 

 auriculo-ventricular, is placed in front and to the right of that opening, 

 and very close to it, being separated from it only by the attachment of 

 the anterior segment of the mitral valve. The semilunar valves which 

 guard it are thicker and stronger than those of the right side of the heart, 

 the lunulse are more strongly marked off, and the central nodules, or corpora 

 Arantii, are larger. The sinuses of Valsalva are more strongly marked at 

 the mouth of the aorta than at the commencement of the pulmonary artery, 

 and from the two anterior of them arise the right and left coronary 

 arteries for the supply of blood to the substance of the heart. 



POSITION OF THE PARTS OF THE HEART WITH RELATION TO THE WALL 



OF THE THORAX. 



The exact position of the various parts of the heart is important in 

 reference to auscultation. This subject has of late been carefully investigated 

 by several anatomists ; but there is still some discordance in their state- 

 ments on some points, caused probably by the difficulty of marking with 

 precision the situation of non-symmetrical viscera in artificially opened 

 bodies, and in part perhaps by differences naturally existing among indi- 

 viduals. The following statement derived from Luschka is in general accor- 

 dance with the results of others, with the exception, as remarked by Walshe, 

 that most of the positions are fixed a little too high. Nearly two-thirds of 

 the bulk of the heart lie to the left of the middle line. The upper edge 

 of the auricles corresponds with a line extending across the sternum from 

 the second right into the first left intercostal space. The auriculo-ventricular 

 sulcus corresponds with a line which unites the sternal end of the fifth right 

 costal cartilage with the second left intercostal space beneath the middle of 

 the second costal cartilage. The rounded margin formed by the wall of the 



Y 



