278 



THE CIRCULATORY SYSTEM. 



(i.e., it lies against the septum), while of the two others which 

 do not lie against the septum, one is dorsal {d") and the other 

 ventral. Each flap is thin, semicircular, and membranous, and 

 is attached to the border of the auriculoventricular opening by 

 the diameter of the semicircle. The free border of each is 

 attached to the wall of the heart by numerous delicate ten- 

 dinous bands, the chordae tendineae (r), some of which are 

 attached to the lower face of each valve. The chordae tendineae 



Fig. 117.— Heart, with Right Ventricle laid open to show the Tri- 

 cuspid Valve. 



a, trabeculre; b, columnre carnere; c, chordre tendinere; (/, </', </", the three flaps 

 of the tricuspid valve; e, aorta; /, conus arteriosus, laid open; g, semilunar valves 

 of the pulmonary artery. 



of the septal valve (or most of them) are attached at their 

 opposite ends to the septum directly, while those of the dorsal 

 and ventral flaps are attached to the ends of three or more 

 band-like muscles, columnae (or trabecuL-e) carneae {b), which 

 are fixed by their opposite ends to the ventricular wall. 



Between the conus arteriosus (/) and the pulmonary artery 

 are three pocket-like semilunar valves (Fig. 117, ^), one ven- 

 tral, one dextral, and one sinistral. Between each valve and 

 the wall of the pulmonary artery there is an enlargement of the 

 cavity of the artery, one of the pulmonary sinuses (or sinuses 

 of Valsalva). Beyond the sinuses the pulmonary artery divides 

 into right and left branches (Fig. 116,7). 



