THE LEFT VENTRICLE. 



2i9 



lunated depression may be observed (1'), comparable to a mark made 

 by the finger-nail on a soft surface. This is the vestige of the 

 foramen ovale, as it appears on the left side. The depression is limited 

 by a slight crescentic ridge, the concavity of which is turned upwards, 

 and which is in fact the border of the now adherent membranous valve, 

 which during foetal life is applied to the left side of the then open 

 foramen ovale. The line of adhesion may vary so as to leave more or 

 less of a pocket-like recess. 



Fig. 170. — The Left Auricle Fig. 170. 



AND Ventricle opened and 



A I'ART OF the WaLL Re- 



jioved so as to show theik 

 Interior (Allen Thom- 

 son). One-half the natur- 

 al size. 



The commencement of the 

 pulmonary artery has been cut 

 away, so as to show the aorta : 

 the opening into the left ven- 

 tricle has been carried a short 

 distance into the aoi-ta between 

 two of the semilunar flaps ; 

 jiart of the auricle with its 

 appendix lias been removed. 

 1, the two right inilmouary 

 veins cut short ; 1', placed 

 within the cavity of the 

 auricle on the left side of the 

 septum and on the part which 

 fbrms the remains of the valve 

 of the foramen ovale, of 

 which the crescentic border is 

 seen ; 2', a narrow portion 

 of the wall of the auricle and 

 ventricle preserved around the 

 auriculo-ventricular orifice ; 3, 

 the left ijart, 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 wall of the left ventricle 

 which has been preserved with 

 the jirincipal anterior or left 

 papillary muscle attached to 

 it ; 5, 5, the large jiosterior or 3 ' 



right papillary muscles ; 5', the 



left side of the septum ventriculorum : li, the right or aortic segment, and 6', the left or 

 liarietal segment of the mitral valve ; 7, placed in the interior of the aorta near its com- 

 mencement and above its valve ; 7', the exterior of the great aortic sinus ; 8, the upj^er 

 part of the conus arteriosus with the root of the pulmonary artery and its semilunar 

 valves ; 8', the sejiarated 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. 



The left or posterior ventricle occupies the left border of the 

 heart, but only about a third of its extent appears on the anterior sur- 

 face, the rest })eing seen behind. It is longer and narrower than the right 

 ventricle, and the cross section of its cavity is oval, not crescentic, the 

 septum on this side being concave (fig. 1G9). Its walls, which, excepting 



