98 



THE VASCULAR SYSTEM 



the heart, the connective tissue is still more abundant, and may 

 contain groups of fat cells. It is through these accumulations of 

 connective tissue that the larger blood vessels are distributed to 

 the myocardium. 



Epicardium. The epicardium, like the other serous mem- 

 branes, consists of a layer of pavement cells, so joined edge to 



edge as to form a complete 

 endothelial coat. Here and 

 there the endothelium pre- 

 sents small openings at the 

 angles between its cells ; 

 these stomata are surround- 

 ed by minute, finely granu- 

 lar cells and are connected 

 with the lymphatic vessels. 

 The endothelium of the 



a, endothelium ; 6, connective tissue, 

 and eosin. Photo, x 500. 



FIG. 97. THE PARIETAL LAYER OF THE PERI- 

 CARDIUM OF A CHILD. 



Hematein epicardium is supported 

 upon a thin layer of dense 

 areolar tissue in which are 



many small blood vessels and lymphatics. Fibres from the deeper 

 surface of this layer are prolonged into the myocardium to become 

 continuous with its endomysial connective tissue. The larger of 

 these connective tissue trabeculae accompany the branches of the 

 larger arteries and veins which are distributed to the muscular 

 wall of the heart. 



FIG. 98. THE ENDOCARDIUM. 

 From the ventricular wall of the heart of man. Hematein and eosin. 



Photo, x 469. 



Endocardium. The endocardium consists of a lining mem- 

 brane of polygonal endothelial cells supported upon a thin layer 



