2l6 



HUMAN PHYSIOLOGY 



and outer part of the ring, and hangs down into the posterior 

 part of the ventricle. It is connected by its anterior margin 

 with the anterior papillary muscle and by its posterior margin 

 with the posterior papillary muscle. Contraction of these 

 muscles will therefore approximate its anterior edge to the 

 infundibular cusp, its posterior edge to the septal cusp. 



In both the infundibular and posterior cusps many of the 

 chordae pass up to be inserted into the auriculo-ventricular 

 ring. 



Semilunar Valves. The valves, situated at the opening 



PA 



PPM 



FlO. 107. The Right Ventricle and Tricuspid Valve to show relationship of the 

 Papillary Muscles and Chorda Tendineae to the Cusps of the Valve. (See text.) 



of the ventricles into the great arteries, are also formed as 

 special developments of the endocardium. 



Each is composed of three half-moon-shaped membranous 

 pouches attached along their curved margin to the walls of 

 the artery and upper part of the ventricle, and with their 

 concavities directed away from the ventricle. In the centre 

 of the free margin is a fibrous thickened nodule, the corpus 

 Arantii, from which a very thin piece of membrane, the 

 lunule, extends to the attached margin of the edges. A 

 pouch, the sinus of Valsalva, lies behind each cusp. 



The arrangements of these various cusps is of importance 

 in connection with their action (Fig. 108). 



