THE HEART. 



1093 



The mitral or bicuspid valve is attached to the circumference of the auriculo- 

 ventricular orifice in the same way that the tricuspid valve is on the opposite side. 

 It is formed by fibrous membrane covered on both surfaces by endocardium, and 

 contains a few muscular fibres. It is large in size, thicker, and altogether stronger 

 than the tricuspid, and consists of two segments of unequal size. The large seg- 

 ment is placed in front and to the right, between the auriculo-ventricular and 

 aortic orifices. Two smaller segments are usually found at the angles of junction 

 of the larger. Similar segments are less constantly found between the main ones 

 of the tricuspid valve. The mitral valve-flaps are furnished with chordae tendinese, 

 the mode of attachment of which. is precisely similar to that of those on the right 

 side, but they are thicker, stronger, and less numerous. 



The semilunar valves surround the orifice of the aorta ; two are posterior (right 

 and left), and one anterior ; they are similar in structure and mode of attachment to 

 the pulmonary valves. They are, however, larger, thicker, and stronger, the lunulae 

 are more distinct, and the corpora Arantii larger and more prominent. Between each 

 valve and the cylinder of the aorta is a deep depression, the sinus aortici (sinuses 

 of Valsalva) ; they are larger than those of the root of the pulmonary artery. The 

 right coronary artery arises from the anterior ; the left from the left posterior. 



The columnce carnece admit of a subdivision into three sets, like those upon the 

 right side, but they are smaller, more numerous, and present a dense interlace- 

 ment, especially at the apex and upon the posterior wall. Those attached by one 

 extremity only, the musculi papillares, are two in number, being connected one to 



Vena cava inf. Right inf. puJm. vein 



\ 



EiistacJtinn riilr 



Valve of 



Thebesiits 



Trabeculx 



Left inf. 

 pulm. vein 



Coronary 

 mlcus 



Chordse tendin. 



Muse, papill. 



Muse. pupil!. 



FIG. 697. Section of the heart, showing the inturarticular and interventricular septa. (Gegenbaur.) 



the anterior, the other to the posterior wall ; they are of large size, and terminate 

 by free rounded extremities from which the chordae tendineae arise. 



The septum between the two ventricles is thick, especially below (Fig. 697)- 



