THE LEFT AURICLE. 



311 



delicate than those which guard the aorta ; and the sinuses of Valsalva are 

 less strongly marked. 



3. The LEFT AURICLE occupies the left and posterior part of the base of 

 the hearfc. When distended, the atrium presents from behind, where it is 

 best seen, a quadrilateral appearance. In front it rests against the aorta 

 and pulmonary artery ; behind, on each side, it receives two pulmonary 

 veins, those from the left lung entering very clo-e together ; and on the 

 right it is in contact with the other auricle. The auricular appendage is 



Fig. 233. THE LEFT AURTCLE Fig. 233. 



AND VENTRICLE OPENED AND 

 A PART OP THEIR ANTERIOR 

 AND LEFT WALLS RKMOVKD 

 SO AS TO SHOW THEIR IN- 

 TERIOR. | 



The pulmonary artery Las 

 been divided at its commence- 

 ineut so as to show the aorta : 

 the opening into the left ven- 

 tricle has been carried a short 

 distance into the aorta between 

 two of the segments of the 

 semilunar valves ; the left 

 part of the auricle with its 

 appendix has been removed. 

 The right auricle lias been 

 thrown out of view. 1, the 

 two right pulmonary veins cut 

 short : their openings are seen 

 within the auricle; 1', placed 

 within the cavity of the auricle 

 on the left side of the septum 

 and on the part which forms 

 the remains of the valve of the 

 foramen ovale, of which the 

 crescentic fold is seen towards 

 the left hand of 1 ; 2', a narrow 

 portion of the wall of the auricle 

 and ventricle preserved round 

 the auriculo-ventricular orifice; 

 3, the left part, 3', the right 

 part towards the septum of the 

 cut surface of the wall of the 

 ventricle, seen to become very 

 much thinner towards 3", at 

 the apex ; 4, a small part of 

 the anterior wall of the left 

 ventricle which has beeu pre- 

 served with the principal an- 

 terior columna carnea attached to it ; 5, 5, the large posterior columnse Caracas ; 5', the 

 left side of the septum within the cavity of the left ventricle ; 6, the right or aortic seg- 

 ment, and 6', the left or parietal segment of the mitral valve; 7, placed in the interior of 

 the aorta near its commencement and above the three segments of its semilunar valve which 

 are hanging loosely together ; 7', the exterior of the great aortic sinus ; 8, the upper part 

 of the conus arteriosus with the root of the pulmonary artery and its semilunar valves ; 

 8', the separated portion of th e pulmonary artery remaining attached to the aorta by 9, 

 the cord of the ductus arteriosus ; 10, the arteries rising from the summit of the aortic 

 arch. 



the only part of the left auricle seen from the front : it extends forwards 

 from the left side of the atrium, and curves towards the right side, resting 



