LEFT VENTRICLE. 537 



The Pulmonary veins, two from the right and two from the left 

 lung, open into the corresponding sides of the auricle. The two left 

 pulmonary veins terminate frequently by a common opening. 



The Auricula-ventricular opening is the aperture of communication 

 between the auricle and ventricle. 



The Musculi pectinati are fewer in number than in the right auricle, 

 and are situated only in the appendix auriculae. 



LEFT VENTRICLE. The left ventricle is to be opened by making 

 an incision a little to the left of the septum ventriculorum, and con- 

 tinuing it around the apex of the heart to the auriculo-ventricular 

 opening behind. 



The left ventricle is conical, both in external figure and in the form 

 of its internal cavity. It forms the apex of the heart, by projecting 

 beyond the right ventricle, while the latter has the advantage in 

 length towards the base. Its walls are about seven lines in thick- 

 ness, those of the right ventricle being about two lines and a half. 



It presents for examination, in its interior, two openings, two 

 valves, and the tendinous cords and muscular columns ; they may be 

 thus arranged : 



Auriculo-ventricular opening, 

 Aortic opening. 



Mitral valves, 

 Semilunar valves. 



Chordae tendineae, 

 Columnae carneae. 



The Auriculo-ventricular opening is a dense fibrous ring, covered by 

 the lining membrane of the heart, but smaller in size than that of the 

 right side. 



The Mitral valves are attached around the auriculo-ventricular 

 opening, as are the tricuspid in the right ventricle. They are thicker 

 than the tricuspid, and consist of only two segments, of which the 

 larger is placed between the auriculo-ventricular opening and the com- 

 mencement of the aorta, and acts the part of a valve to that foramen 

 during the filling of the ventricle. The difference in size of the two 

 valves, both being triangular, and the space between them, has given 

 rise to the idea of a " bishop^s mitre," after which they were named. 

 These valves, like the tricuspid, are furnished with an apparatus of 

 tendinous cords, chordce tendinece, which are attached to two very large 

 columnce carnece. 



The Columnce carnece admit of the same arrangement into three 

 kinds, as on the right side. Those which are free by one extremity, 

 the columnae papillares, are two in number, and larger than those on 

 the opposite side ; one being placed on the left wall of the ventricle, 

 and the other at the junction of the septum ventriculorum with the 

 posterior wall. 



