EPITHELIAL AND ENDOTHELIAL TISSUE. 



335 





Wedl, the lymphatics are very numerous in the fat-tissue lying 

 beneath the visceral layer of the pericardium. 



The nerves of the heart are of both the medullated and non- 

 medullated varieties. The 

 former are branches of the 

 vagus nerve, the latter of 

 the sympathetic system ; jr- 

 the plexus cardiacus is a 

 combination of both. The 

 subserous branches accom- 

 pany the coronary vessels 

 in plexiform arrangement, 

 and are studded with gan- 

 glionic elements, single or 

 in groups. The termina- 

 tion of the nerves in the 

 muscle of the heart has not 

 yet been demonstrated. 



(2) The Arteries. Their 

 walls are composed of at 

 least three layers, the inner 

 of which the intima is 

 endothelium; the middle 

 the media smooth mus- 

 cle ; and the outer the 

 adventitia a connective- 

 tissue formation. These 

 three layers are very firmly 

 connected with each other ; 

 the relative thickness of 

 these coats varies greatly 

 with the size and the loca- 

 tion of the vessel. (See 

 Fig. 144.) 



The inner coat is com- 

 posed of flat, nucleated 



FIG. 144. WALL OF THE EXTERNAL CAR- 

 OTID OF MAN. TRANSVERSE SECTION. 

 endothelia, exhibiting the 

 usual bioplasson reticu- 

 lum. These bodies are 

 elongated in the longitudi- 

 nal direction of the artery, 

 and in edge view appear spindle-shaped, owing to their middle 



E, endothelial layer, beneath which is a hyaline, 

 so-called elastic, layer ; MM, smooth muscle in lon- 

 gitudinal and transverse section ; F, dense fibrous 

 connective tissue, with a network of broad elastic 

 fibers ; C, loose connectiA'e tissue supplied with capil- 

 lary blood-vessels. Magnified 200 diameters. 



