396 ANGIOLOGY. 



are arranged in two sets, one common to both, and another proper 

 to each ventricle, thus forming as it were two muscular sacs 

 enclosed in a third. The fibres, whether common or proper, are 

 attached directly or indirectly by both extremities to the tendin- 

 ous rings. The common fibres are arranged in successive layers, 

 arising from the auriculo-ventricular ring. They extend spirally 

 from above downwards, on the anterior surface from right to left, 

 on the posterior from left to right. They are thin and broad at 

 the upper part of the ventricles, becoming thick and narrow as 

 they reach the apex, where they encoil, forming a whorl, then 

 penetrate beneath the layers, and pass up internally, forming the 

 walls and septum, terminating on the auriculo-ventricular ring. 

 The common fibres thus form a superficial layer, passing down- 

 wards, and a deep layer reflected upwards, between which are 

 enclosed the layers special to each ventricle. The special fibres 

 form circular or curved bands, inserted by both extremities to the 

 tendinous rings. 



The heart is supplied with blood by the coronary arteries, 

 which arise from the sinuses of Valsalva. The blood is returned 

 by the coronary veins which pass to the coronary sinus, and the 

 venaB cordis minimae, which terminate in the foramina Thebesii. 

 The nerves of the heart come chiefly from the cardiac plexus, 

 formed by the sympathetic and the vagus. The lymphatics 

 follow the course of the blood-vessels, and terminate in glands at 

 the base of the heart. 



ENDOCAEDIUM. 



The cavities of the heart are all lined by the serous endocar- 

 dium, which is continuous with the lining membrane of the blood- 

 vessels. It is thin, smooth, and glistening, giving a polished 

 appearance to the inside of the heart, to which it adheres by 

 cellular tissue. It enters into the formation of the valves, being 

 strengthened by fibrous and muscular tissue between its folds. 

 It is rather red in colour on the right side. 



So far as the heart itself is concerned, since, in the adult, the 

 right side is separate from the left, there are two Endocardia, but 

 as the lining membrane of the arteries is continuous through the 

 capillaries with that of the veins, the two membranes ultimately 

 form a continuous structure. 



