94 THE CIRCULATION. 



portions, so as to form an annular membrane around the auric- 

 ulo- ventricular opening, being fixed to a tendinous ring, which 

 encircles the orifice between the auricle and ventricle, and 

 receives the insertions of the muscular fibres of both. In each 

 principal portion of the valve may be distinguished a middle- 

 piece, extending from its base to its apex, and including about 

 half its width; this piece is thicker, and much tougher and 

 tighter than the border-pieces, which are attached loose and 

 flapping at its sides. 



While the bases of the several portions of the valves are 

 fixed to the tendinous rings, their ventricular surfaces and 

 borders are fastened by slender tendinous fibres, the chorda 

 tendinece, to the walls of the ventricles, the muscular fibres of 

 which project into the ventricular cavity in the form of bun- 

 dles or columns the columnce carnece. These columns are not 

 all of them alike, for while some of them are attached along 

 their whole length on one side, and by their extremities, 

 others are attached only by their extremities ; and a third set, 

 to which the name musculi papillares has been given, are at- 

 tached to the wall of the ventricle by one extremity only, the 

 other projecting, papilla-like, into the cavity of the ventricle 

 (5, Fig. 35), and having attached to it chordce tendinece. Of 

 the tendinous cords, besides those which pass from the walls 

 of the ventricle and the musculi papillares, to the margins of 

 the valves both free and attached, there are some of especial 

 strength, which pass from the same parts to the edges of the mid- 

 dle pieces of the several chief portions of the valve. The ends of 

 these cords are spread out in the substance of the valve, giving 

 its middle-piece its peculiar strength and toughness ; and from 

 the sides numerous other more slender and branching cords 

 are given off, which are attached all over the ventricular sur- 

 face of the adjacent border-pieces of the principal portions of 

 the valves, as well as to those smaller portions which have 

 been mentioned as lying between each two principal ones. 

 Moreover, the musculi papillares are so placed that from the 

 summit of each tendinous cords may proceed to the adjacent 

 halves of two of the principal divisions, and to one interme- 

 diate or smaller division, of the valve. 



It has been already said that while the ventricles communi- 

 cate, on the one hand, with the auricles, they communicate, on 

 the other, with the large arteries which convey the blood away 

 from the heart ; the right ventricle with the pulmonary artery 

 (6, Fig. 34), which conveys blood to the lungs, and the left 

 ventricle with the aorta, which distributes it to the general 

 system (7, Fig. 35). And as the auriculo-ventricular orifice 



