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HAND-BOOK OF PHYSIOLOGY. 



Left Auricle. The left auricle is situated at the left and posterior 

 part of the base of the heart, and is best seen from behind. It is quadri- 

 lateral, and receives on either side two pulmonary veins. The auricular 

 appendix is the only part of the auricle seen from the front, and corre- 



FIG. 93. The left auricle and ventricle opened, and a part of their anterior and left walls re- 

 moved. H- The pulmonary artery has been divided at its commencement; the opening into the left 

 ventricle carried a short distance into the aorta between two of the segments of the sernilunar valves, 

 and the left part of the auricle with its appendix has been removed. The right auricle is 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 re- 

 mains of the valve of the foramen ovale, of which the crescentic fold is seen toward the left hand of 

 1' ; 2, a narrow portion of the wall of the auricle and ventricle preserved round the auriculo- ven- 

 tricular 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 pre- 

 served with the principal anterior columna carnea or musculus papillaris attached to it; 5, 5, musculi 

 papillares; 5', the left side of the septum, between the two ventricles, 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 hanging loosely together; 7', the exterior 

 of the great aortic sinus ; 8, the root of the pulmonary artery and its semilunar valves ; 8'. the sepa- 

 rated 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 aortic arch. (Allen Thomson.) 



spends with that on the right side, but is thicker, and the interior is more 

 smooth. The left auricle is only slightly thicker than the right, the dif- 

 ference being as 1 J lines to 1 line. The left auriculo-ventricular orifice 

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



