THE HEART. 



the musculi papillares there is a large anterior one whose cords 

 go to the right and left cusps of the tricuspid valve; a smaller 

 and posterior one whose cords go to the right and posterior 

 cusps; and a varying group of bundles whose cords go to the 

 left and posterior cusps. [789] 



The tricuspid orifice opens into the body and has a valve 

 (tricuspid) with three cusps, right, left, and posterior. The 

 cusps are doubled endocardial folds, with intermediate fibrous 

 tissue, and thinnest at their free margin; they are usually 

 continuous at the margins of the orifice, where they are at- 

 tached to a fibrous ring. Their apices hang down ; the chordae 

 tendinese are attached to the margins, apices, and ventricular 

 surfaces. The pulmonary orifice lies in front of the tricuspid 

 and opens from the infundibulum into the pulmonary artery. 

 It has a valve (pulmonary) composed of three semilunar seg- 

 ments, posterior and two anterior, which are formed of fibrous 

 tissue between an endocardial layer and one derived from the 

 inner arterial coat. The outer border of each segment is at- 

 tached to the arterial wall; the inner border is free and pre- 

 sents a small nodule (corpus Arantii) mesially, and on each 

 side of this a thin and semilunar segment (lunule) . [789] 



Interior of Left Ventricle. The cavity is conical and sepa- 

 rable into a body and a small aortic vestibule; the latter lies 

 just below the aortic orifice. Many fine columnse carnese of 

 the first two kinds are seen on the inferior wall and apex; 

 there are two large musculi papillares, anterior and posterior, 

 with chordse tendinea going to both cusps of the mitral valve. 

 The mitral orifice opens into the body. It has a valve (mitral) 

 with two triangular cusps; a smaller one (marginal) lying to 

 the left and behind; and a larger one (aortic) lying to the 

 right and in front, toward the aortic orifice. The bases of the 

 cusps are either continuous at their attachment to the fibrous 

 ring round the orifice, or separated by small intermediate 

 cusps ; the apices hang down. Their structure and the attach- 

 ment of the chordse tendineae is similar to that of the tricuspid 



[127] 



