MINUTE ANATOMY OF THE HEART. 255 



The pericardium, in opposition to the endocardium, is a serous 

 membrane, and possesses the general characteristic peculiarities 

 of such membranes. The subserous tissue is occasionally marked 

 by the presence of a large number of fat cells. 



The bloodvessels are branches of the coronary arteries, and are 

 distributed in the muscular substance, as well as to the pericar- 

 dium and endocardium. The vessels of the last-named membrane 

 extend, according to Luschka, into the valves. The capillary ves- 

 sels distributed through the muscular substance of the heart are 

 very numerous, the muscle cells themselves being enclosed in a 

 network of vessels. The rootlets of the veins are formed by 

 several capillary vessels uniting directly to form a thicker 

 trunk ; an arrangement by which, we may conclude, the dis- 

 charge of the blood is facilitated. 



In reference to the lymphatics of the heart, we possess recent 

 investigations byEberth and Belajeff;* and, as they have pointed 

 out, a network of lymph capillaries of the ordinary kind may be 

 distinguished both in the pericardium as well as in the endocar- 

 dium, the meshes of which are sometimes large and sometimes 

 small, and are usually arranged in a single layer, but occasionally, 

 where the thickness of the membrane is considerable, in several 

 layers. The endocardial lymphatic network of the auricle is con- 

 tinued by means of a few finer tubes upon the auriculo-ventricular 

 valves, and reaches nearly to their middle. In the same way a 

 few lymph tubes may be traced as prolongations of the network 

 of the endocardium of the ventricle into the semi-lunar valves. 

 In the muscular substance of the heart itself the above-named 

 observers found, in opposition to Luschka, that the lymphjvessels 

 were " not so numerous," whilst I conclude, from my own re- 

 searches, that the muscular substance of the heart stands in 

 still closer relation to the lymphatics than appears from their 

 statement, because I am of opinion that the formerly described 

 fissures of Henle found in the muscular substance must be re- 

 garded as a portion and continuation of the lymphatic system. 

 But since these fissures are connected at many points with 

 one another, they form a canal system, permeating the muscular 

 substance to an extent which certainly cannot be termed sparing. 



* Virchow's Archiu, Band xxxvii., p. 124. 



