THE LEFT VENTRICLE. 463 



opening between the two. In the foetus only a very small quantity in foetus, 

 of blood passes through the lungs ; and the left auricle receives its 

 pure blood from the inferior vena cava through the right auricle by 

 the aperture in the septum (foramen ovale). 



Dissection. The left ventricle may be opened by an incision How to 

 along both the anterior and the posterior surfaces, near the septum ; ventricle 

 these are to be joined at the apex, but are not to be extended 

 upwards so as to reach the auricle. Oil raising the triangular flap 

 the interior of the cavity will be visible. 



The CAVITY OF THE LEFT VENTRICLE is longer and more conical Form of left 

 in shape than that of the opposite ventricle ; and it is oval, or almost N en 

 circular, on a transverse section. 



The apex of the cavity reaches the apex of the heart. The base Apex, 

 is turned towards the auricle ; and in it are the openings into the Base with 

 aorta and the left auricle. openings. 



The icaU of this ventricle is much thicker than that of the right, Wall, 

 and the anterior boundary is formed for the most part by the inter- 

 ventricular septum. 



Its surface is irregular, like that of the right ventricle, in con- inner sur- 

 sequence of the projection of the columnae carnese ; but near the fl a ^l has 

 aorta the surface is smoother. There are three kinds of fleshy columns columns, 

 in this as in the right ventricle. The large musculi papillo.res give and some 

 attachment to the tendinous cords of the auriculo-ventricular valve, verj ' lar s e - 

 and are more strongly marked than on the right side : they are 

 arranged in two great bundles, which spring from the right and left 

 sides of the cavity. 



The left auricula -ventricular opening is placed beneath the orifice Leftauri- 

 of the aorta, but close to it, only a thin fibrous band intervening JJj 

 between the two. It is rather smaller than the corresponding ture : 

 aperture of the right side, being about three inches and a half in form and 

 circumference, and it is longest in the transverse direction. It is size 5 

 furnished with a membranous valve (mitral) which projects into 

 the ventricle. 



The mitral mice is stronger and of greater length than the tri- Mitral 

 cuspid, and has also firmer and more tendinous cords ; it takes its valve: 

 name from a fancied resemblance to a mitre. Attached to a fibrous 

 ring round the aperture, it is divided below by a notch on each 

 side into two pieces. Its segments lie one before the other, with 

 their edges directed to the sides, and their surfaces towards the 

 front and back of the cavity. The anterior, or aortic cusji, of the aortic cusp; 

 valve intervenes between the auricular and aortic openings, and is 

 larger and looser than the posterior or marginal cusp. 



The mitral resembles the tricuspid valve in its structure and structure; 

 office. Its segments consist of thicker and thinner parts ; and in 

 the notches at the sides there are also thinner pieces between the 

 two primary segments. The chordae tendinae ascend to be attachment 

 attached to the valve in the notches between the tongues; and of cords ' 

 they end on the segments in the same way as in the tricuspid valve. 

 Each of the large papillary muscles acts on both portions of the 

 valve. 



