110 HAND-BOOK OF PHYSIOLOGY. 



tendinous rings, their ventricular surfaces and borders are fastened by 

 slender tendinous fibres, the cliordce tendinece, to the walls of the ventri- 

 cles, the muscular fibres of which project into the ventricular cavity in 

 the form of bundles or columns the columncs 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 attached to the wall of the ventricle by 

 one extremity only, the other projecting, papilla-like, into the cavity of 

 the ventricle (5, Fig. 93), and having attached to it clwrdce tendinew. 

 Of the tendinous cords, besides those which pass from the walls of the 

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

 are some of especial strength, which pass from the same parts to the edges 

 of the middle and thicker portions of the cusps before referred to. 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 surface 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 proceed to the adjacent halves of two of the prin- 

 cipal divisions, and to one intermediate or smaller division, of the valve. 



The preceding description applies equally to the mitral and tricuspid 

 valve; but it should be added that the mitral is considerably thicker and 

 stronger than the tricuspid, in accordance with the greater force which 

 it is called upon to resist. 



It has been already said that while the ventricles communicate, 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 ven- 

 tricle with the pulmonary artery (6, Fig. 93), which conveys blood to the 

 lungs, and the left ventricle with the aorta, which distributes it to the 

 general system (7, Fig. 93). And as the auriculo-ventricular orifice is 

 guarded by valves, so are also the mouths of the pulmonary artery, and 

 aorta (Figs. 93, 99). 



The semilunar valves, three in number, guard the orifice of each of 

 these two arteries. They are nearly alike on both sides of the heart; but 

 those of the aorta are altogether thicker and more strongly constructed 

 than those of the pulmonary artery, in accordance with the greater pres- 

 sure which they have to withstand. Each valve is of semilunar shape, its 

 convex margin being attached to a fibrous ring at the place of junction 

 of the artery to the ventricle, .and the concave or nearly straight border 

 being free, so that each valve forms a little pouch like a watch-pocket 

 (7, Fig. 93). In the centre of the free edge of the valve, which contains 



