HEART. 119 



To expose the left ventricle, make a short incision into it with, a 

 knife close to the septum ; pass the finger through this into the aorta, 

 and upon it, as a director, divide the ventricle and aorta with the 

 scissors, keeping close to the septum, passing between the two ap- 

 pendices auriculae, and holding aside the pulmonary artery, so as not 

 to injure that vessel in making the section. 



The LEFT VENTRICLE is more conical in shape than the 

 right, and its walls are twice as thick and much more 

 muscular; its surface is irregular from the columnar carnese, 

 but near where the aorta arises the walls are smooth. 



The mitral valve will have been left undivided if the 

 ventricle is opened as has been directed. It consists of 

 two folds of the lining membrane, attached to the anriculo- 

 ventricular orifice, and connected to the columnre carnea? 

 by chordae tendinere in a manner similar to that described 

 as existing upon the right side. The chordae tendinese 

 converge to be inserted in two distinct bundles into the 

 columnar carnese ; they are stronger, but less numerous, 

 than those of the right ventricle, and the same may be said 

 of the columnaa cameae. 1 



The septum ventriculorum seems to form part of the left 

 rather than of the right ventricle, being concave on its left 

 and convex on its right side. 



The aortic semilunar valves are found at the commence- 

 ment of the aorta, nearly on a level with the mitral valve. 

 They are stronger, though similar in number and in general 

 shape to those of the pulmonary artery ; the corpora Arantii 

 are more developed, and the dilatations of the vessel behind 

 each segment are much more pronounced ; they are here 

 called the aortic sinuses, or sinuses of Valsalva. 



The orifices marking the origin of the anterior and pos- 

 terior coronary arteries will be observed just behind the 

 semilunar valves. Occasionally, these arteries arise from a 

 common trunk, and their number is sometimes increased to 

 three. Their course has been described (p. 116). 



The student should at some time avail himself of an opportunity 

 to examine the interior of the heart, prepared after the following me- 

 thod. Having washed out the blood and fibrin contained in its cavi- 

 ties, they are to be distended, by filling them from a syringe, with 

 undiluted alcohol, and confining it there by tying all the vessels ; 

 then immersing the whole organ in a jar filled with alcohol, in a few 



1 The letters L. M. (so familiar in another connection) will give the 

 student a mnemonic key to the side to which the mitral valve belongs. 

 (L. M., left, mitral.) 



