STRUCTURE OF HEARTHS VALVES. 



95 



is guarded by valves, so are also the mouths of the pulmonary 

 artery and aorta (Figs. 34, 35). 



FIG. 35. 



The left auricle and ventricle opened and a part of their anterior and left walls 

 removed so as to show their interior. %. The pulmonary artery has been divided 

 at its commencement so as to show the aorta ; the opening into the left ventricle 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 has 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 re- 

 mains 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 pre- 

 served round the auriculo-ventricular orifice; 3, 3', the cut surface of the walls 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 been preserved with the 



