LEFT VENTRICLE. 481 



sinuses are situated behind the valves at the commencement of the aorta, 

 and are larger and more capacious than those of the pulmonary artery. 



The Pulmonary artery commences by a scalloped border, correspond- 

 ing with the three valves which are attached along its edge. It is con- 

 nected to the ventricle by muscular fibres, and by the lining membrane of 

 the heart. 



The LEFT AURICLE is somewhat smaller, but thicker, than the right ; 

 of a cuboid form, and situated more posteriorly. The appendix auricula 

 is constricted at its junction with the auricle, and has a foliated appear- . 

 ance ; it is directed forwards towards the root of the pulmonary artery, to 

 which the auriculae of both sides appear to converge. 



The left auricle is to be laid open by a - 1 - shaped incision, the horizontal 

 section being made along the border, which is attached to the base of the 

 ventricle. It presents for examination five openings, and the muscular 

 structure of the appendix ; these are 



Four pulmonary veins, 

 Auric ulo- ventricular opening, 

 Musculi pectinati. 



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 be- 

 tween the auricle and ventricle. 



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

 Are situated only in the appendix auricula?. 



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

 incision a little to the left of the septum ventriculoram, and continuing it 

 around the apex of the heart to the auriculo-ventricuiar 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 thickness, 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; the} may be thus 

 arranged : 



Auriculo-ventricuiar opening, 



Aortic opening. 



Mitral valves, 



Semilunar valves. 



Chorda? tendineae, 



Columns carnese. 



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

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

 side. 



The Mitral valves are attached around the auriculo-ventricuiar opening, . 

 as are the tricuspid in the right ventricle. They are thicker than the tri- 

 cuspid, and consist of only two segments, of which the larger is placed 

 41 2r 



