THE VESSELS. 293 



6. the left appendix; 7. the right auricle; 8. the superior cava; 9. the left 

 auricle ; 10. the pulmonary veins (Blandin). 



Structure. The chief mass of the heart consists of round and flat muscular 

 bands (transversely striated fibres), which are throughout separated into two 

 halves, lying evenly close to one another on the outer surface, projecting 

 irregularly on the inside of the cavity, as they are either firmly attached at 

 both extremities (fleshy bands, trabecula carnecB [musculi pectinati]), or the 

 free pointed extremity is turned to the basis of the heart (mm. papillares [car- 

 nee columnee] ). In the ventricles the muscular layer is as thick as eight lines ; 

 at places in the ventricles extremely thin. Fibro-cartilaginous filaments se- 

 parate the auricles as well as the ventricles (in the septa) from one another, 

 and the auricles from the ventricles (in the circular groove). The outer cover- 

 ing is formed from the internal layer of the pericardium, and attached by 

 fibro-cellular, containing adipose tissue. Fat is found, particularly in aged 

 (also in lean) individuals on both sides of the transverse groove, and along the 

 coronary vessels as far as the apex, especially on the right half of the heart. 

 The internal membrane, endocardium, the immediate continuation of the in- 

 ternal coat of the large venous trunks, lines the cavities of the auricles and 

 ventricles, forms folds at the passage into the latter and in the great arterial 

 trunks, between which two layers, areolar tissue, and fibro-cartilaginous fila- 

 ments, are found. 



These folds projecting into the cavities are the 



Valves, which are free in the mouths of the arteries (a.svalvv.semilunares), 

 in the mouths of the ventricles (as valv. bi- and tricuspidates), are connected 

 by tendinous filaments with the muse, pectin, and column, carnece. 



The internal membrane of the heart is thickest in the auricles. 



Thickness of the walls : 



Left ventricle, in male, 5-^i Par. lin. ; female, 4i 



Septum of ventricles 5 4 



Of right ventricle 2 H 



The cavities and openings of the right half of the heart are wider than those 

 of the left. 



529. Vessels and nerves of the Heart. 



Arteries : coronaria cordis dextra and sinisira from aorta ascendens. 



Veins : coronaria cordis magna and media. 



Lymphatics : accompany the arteries and pass into the lymphatic glands 



above and behind the arcus aorta. 

 Nerves : plexus coronarii accompany the arteries and are then lost in the 



tissue of the heart, arising from plex. cardiacus magnus, and these from 



Nn. cardiaci of N. Vagus and sympathicus. 



530. The Pericardium, 



is a fibro-serous, perfectly closed sac, in which the heart has been so inverted 

 that it is wrapped round as far as its base, and is covered with a serous mem- 



