THE HEART 



145 



In this ventricle are also the projections of the muscular tissue called the 

 columncE carnecB. 



The left auricle is situated at the left and posterior part of the base of 

 the heart. The left auricle is only slightly thicker than the right and its 



FIG. 136. The Left Auricle and Ventricle Opened and a Part of Their Anterior and Left Walls 

 Removed. Magnified . The pulmonary artery has been divided at its commencement; the 

 opening into the left ventricle is carried a short distance into the aorta between two of the segments 

 of the semilunar valves; and the left part 9f the auricle with its appendix has been removed. The 

 right auricle is out of view, i, The two right pulmonary veins cut short; their openings are seen 

 within the auricle; i', 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 toward the left hand of i'; 2, a narrow portion of the wall of the auricle and ventricle preserved 

 round the auriculo- ventricular orifice; 3, 3', the cut surface of the walls of the ventricle, seen to 

 become very much thinner toward 3", at the apex; 4, a small part of the anterior wall of the left 

 ventricle which has been preserved with the principal anterior columna carnea or musculus papil- 

 laris attached to it; 5, 5, musculi papillares; 5', the left side of the septum, between the two ven- 

 tricles, within the cavity of the left ventricle; 6, 6', 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 hang- 

 ing loosely together; 7', the exterior of the great aortic sinus; 8, the root of the pulmonary artery 

 and its semilunar valves; 8', the separated portion of the pulmonary artery remaining attached to 

 the aorta by 9, the cord of the ductus arteriosus; 10, the arteries rising from the summit of the aor- 

 tic arch. (Allen Thomson.) 



form and structure" are the same as in the right. The left auricula-ventricu- 

 lar orifice is oval and a little smaller than that on the right side of the heart. 

 There is a slight vestige on the septum of the foramen between the auricles. 

 10 



