372 THE HEART. 



auricles and are chiefly collected into a trunk which lies in the anterior longitudinal 

 groove, turns to the left around the aorta, and passing between this vessel and the 

 trachea enters the lymphatic gland or glands which are there situated. From these 

 glands the lymph passes into the right innominate vein. Other of the cardiac lym- 

 phatics pass round at the reflection of the pericardium and over the parietal layer to 

 reach the thoracic duct. 



Nerves. The nerves given off by the cardiac plexuses appear rather small in 

 comparison with the bulk of the heart ; they are derived partly from the cerebro- 

 spinal and partly from the sympathetic system (more especially from the pneumo- 

 gastric nerve, and from the cervical and superior thoracic ganglia of the sym- 

 pathetic nerve). 



From the cardiac plexuses at the base of the heart, nerves pass to the auricles 

 and there join a plexus chiefly of non-medullated fibres, which is beset with 

 numerous small groups of ganglion-cells. This gangliated plexus lies for the most 

 part immediately beneath the pericardial covering of the auricles, but its branches 

 penetrate into the muscular substance. 



In the dog's heart Dogiel found three principal groups of ganglia, viz,, one between the 

 superior cava and the right auricular appendix, another between the same vein and the root 

 of the aorta, and a third between the root of the aorta and the pulmonary veins, Schklarewski, 

 in different mammals, describes them as occurring chiefly in the interauricular septum and 

 in the auriculo-ventricular groove. The same is affirmed by Skwartzoff, who, however, found 

 the ganglia on the auricular plexus to be most numerous over the left auricle ; and Vignal 

 states, with regard to the human heart, that it is especially near the orifices of the pulmonary 

 veins that they occur in largest number. 



Nerves are also given off from the cardiac plexuses, which, passing downwards 

 along the commencement of the aorta and pulmonary artery, reach the coronary 

 arteries, and accompanying these in their course form secondary plexuses (right and 

 left coronary plexuses) around those vessels. From the coronary plexuses numerous 

 branches proceed, which pass, for the most part, over the surface of the ventricles 

 under the pericardium, but a few small branches are directed upwards to join the 

 auricular plexus of nerves. Small microscopic groups of ganglion-cells occur, as was 

 shown by Remak, both upon the coronary plexuses and also here and there along 

 their branches for a certain distance. 



The nerve-fibres which pass off from the gangliated plexuses of the auricles and 

 of the base of the ventricles are non-medullated, and are distributed to every part 

 of the muscular tissue of the heart. No ganglia are found upon them, however, in 

 their further course, and no ganglion-cells at all have been found in the apical two- 

 thirds of the ventricles. The nerve-fibres form a close plexus (ground-plexus) 

 amongst the muscular bundles, and from this terminal branches (fibrils) pass off to 

 the muscle-cells, each one ending by a slight enlargement or varicosity of the nerve 

 fibril which is applied to the surface of the cell (laches motrices of Eanvier). 



EPICAKDIUM. 



The cardiac pericardium or epicardium has the usual structure of a serous 

 membrane. It is covered externally by a pavement epithelium (endothelium) of 

 irregularly polygonal cells, and as in other serous membranes stomata are found here 

 and there between these, permitting a communication between the pericardial 

 cavity and the lymphatics of the membrane (Skwartzoff). The substance of the 

 membrane is composed of connective tissue with much elastic tissue, chiefly 

 collected into a well-developed network in the deeper layer (fig. 825, c). 



The subserous areolar tissue is continuous with the interstitial tissue between 



