622 THE HEART. 



by three semilunar valves, having the same provision of 

 corpuscula Arantii and sinuses of Valsalva, but larger and 

 stronger, and having a similar function of preventing the 

 reflux of the blood. The capacity of the different cavities 

 of the heart is very nearly the same, and is estimated at 

 about two ounces. 



Structure. Several elements enter into the composition 

 of the heart. There is first and most external, the reflected 

 serous layer of the pericardium, covering the whole of the 

 outer surface, and already described. On the inner surface, 

 and lining the auricles and ventricles, is seen a very deli- 

 cate and transparent serous membrane, called the endocar- 

 dium. It is strongly attached to the muscular fibres of the 

 columnaa carnese and musculi pectinati, filling up their in- 

 terstices, rendering smooth the whole interior surface of the 

 several cavities, and by its duplications forming the differ- 

 ent valves found between the auricles and ventricles, and 

 at the mouths of the aorta and pulmonary artery. 



Between the outer and inner membrane is situated the 

 muscular structure. This is the most abundant and im- 

 FlG 201. portant element of the heart. 



Its fibres are difficult to 

 trace, and it is advised to 

 submit them to boiling, 

 maceration, putrefaction, 

 and hardening in alcohol, 

 as some of the necessary 

 preparatory means to a suc- 

 cessful dissection. Accord- 

 ing to Cruveilhier, this ele- 

 ment of the ventricles "is 

 composed of two muscular 

 sacs, contained within a 

 third, which is common to both ventricles/' All- the mus- 



FIG. 201 represents the spiral course of the muscular fibres of the Heart, 

 chiefly those of the left ventricle. 1 Left ventricle. 2 Right ventricle. 3 

 Septum of the ventricles. 4 Muscular fibres making a spiral turn around. 5 

 The apex. 



