HEAET 



99 



of delicate fibrous connective tissue. In this membrane is a net- 

 work of elastic fibres. The endothelium of this membrane is con- 

 tinuous with that of those blood vessels which open from the cav- 

 ities of the heart. Its connective tissue also forms a continuous 

 layer with that of the tunica intima of these vessels : in fact, 

 the three coats of the cardiac wall endocardium, myocardium, 

 and epicardium might well be compared with the corresponding 

 three coats of the arterial and venous walls the intima, media, 



A 



FIG. 99. RADIAL SECTIONS OF THE MITRAL VALVE, FROM THE HEART OF A MAN. 



A, from the base of the valve showing the extension into it of cardiac muscle fibres 

 from the wall of the heart; B, from the mid-region of the valve, a, auricular endo- 

 cardium ; 6, muscle fibres ; c, dense fibrous tissue ; d, ventricular endocardium, llcma- 

 tein and eosin. Photo, x 800. 



and adventitia. In either organ, the inner coat consists of a 

 lining membrane of endothelinm, and a supporting membrane of 

 connective tissue; muscle in large part composes the middle 

 coat, while the outer coat is typically a connective tissue layer. 



