Cuspis anterior 



The Heart. 



Cuspis posterior 



375 



Chordae tendineae 



Posterior papillary muscle^ 



-Aunulus fibrosus 



Endocardium 



-Myocardium 



Epicardiuni 



421. Transverse section through the valvula 



bicUSpidalis [mitral is]. The valve is set. 

 (Inferior lialf, viewed from above.) 



The musculi papillares (impillary muscles) (see also Figs. 417, -118, 420, 424 and 425) 

 are more or less isolated, bluntly wedge-shaped elevations of the internal muscular layer of the 

 ventricles. They vary much in size and in dilferent hearts present considerable differences in 

 appearance. From the tip of each muscle there go off one or several tendinous threads (chordae 

 tendineae) of variable strength, which become attached partly to the fi-ee margins (chordae 

 tend, of the I order), partly to the ventricular surface (chordae tend, of the II order) of the 

 cusps of the valves guarding the ostia venosa ; tlie insertion is m the form of a triangular flat 

 expansion. Each papQlary muscle gives off chordae usually to two adjacent cusps. In addition 

 other tendinous threads (chordae tend, of the III order) arise directly from the muscidature 

 of the ventricles and become attached in the same way also to the ventricular surface of the 

 cusps of the valves. The chordae tendineae are of unequal length and are so arranged that 

 the valve is set when they are all put upon the stretch, and vice versa. 



The ralvula tricuspidalis and valvula bicuspidalis [7nitralisJ (see also Figs. 419 and 

 420) consists each of a tube-like membrane, which is attached to the annulus fibrosus (also 

 partly to the wall of the root of the aorta on the left side) and is divided at its free margin 

 by deep incisures into large sails or cusps fcuspides) and by less deep incisures into variably 

 developed, smaller, intemiediary cusps. They are covered on both sides by endocardium and 

 in their peripheral halves contain circular and radial muscle libers which are connected with 

 the musculature of the fore-chambers or atria. At the end of the diastole of the ventricles, the 

 central portions of the atrial surfaces of the cusps become applied to one another (the valves 

 become set); the closure is water-tight and during the systole becomes gradually ever more 

 complete, since the ostia venosa are markedly duninished in size and thus ever larger sections 

 of the cusps of the valves are applied to one another. 



