Chap, x.] THE HEART AND BLOOD-VESSELS. 



75 



vessels, and small branches of nerve-fibres are met 

 with everywhere. The subpericardial and subendo- 

 cardial tissues consist of loosely connected trabeculse 

 of fibrous connective tissue, continuous with the 

 intermuscular connective tissue of the muscular part 

 of the heart. The 

 former contains in 

 many places groups 

 of fat cells. 



96. On the free 

 surface of the papil- 

 lary muscles, in some 

 parts of the surface 

 of the trabeculse 

 carnese, and at the 

 insertion of the 

 valves, the endocar- 

 dium is thickened 

 by tendinous con- 

 nective tissue. The 

 valves themselves 

 are folds of the en- 

 docardium, and con- 

 tain fibrOUS COnneC- Fig. 44. Transverse Section through the 



tive tissue, to which, 



especially in the 



semilunar valves, 



numerous elastic 



fibres are added. The muscular tissue of the wall 



of the auricle penetrates a short way into the auriculo- 



ventricular valves. 



All the cordse tendinese and the valves are of course 

 covered on their free surfaces with endothelium. 



Special tracts of muscle fibres occur in the sub- 

 endocardial tissue. 



The fibres of Purkinje are peculiar fibres occurring 

 in the subendocardial tissue in some mammals and 



Auricle of the Heart of a Child. 



Endothelium lining the endocardium ; 6, en- 

 docardium ; c, muscular bundles cut trans- 

 versely; d, muscular bundles cut longitu- 

 dinally ; e, pericardial covering. 



