CHAP. XXVIII.] NERVES OF THE HEART. 341 



Between the superficial and the deep or reflected portion of the 

 ventricular fibres are some which have been described as the proper 

 fibres of the ventricles ; these pass round each ventricle in a circular 

 direction, some obliquely, some at right angles to its axis ; they 

 form a sort of hollow cylinder for each ventricle, which is attached 

 above to the fibrous zone of the auricles, and is open below towards 

 the apex. On the right side a smaller number of circular fibres 

 embrace the infundibular portion of the ventricle, attaching them- 

 selves to the fibrous festoons of the pulmonary artery. 



Of the Muscular Fibres of the Auricles. In the auricles we 

 find a common and proper set of fibres. The former may be 

 traced along the anterior surface of both auricles, embracing them 

 like a belt, but not extending round to the posterior surface. The 

 latter are arranged in several circular or spiral bands, some of 

 which spring from the auriculo-ventricular zone, and return to 

 it again, and envelop the auricle before and behind, passing 

 sometimes at right angles to it, sometimes obliquely ; others pass 

 round the auricle in a horizontal direction and parallel to the 

 auriculo-ventricular zone. Each of the venous orifices of the 

 auricles is surrounded by a series of circular fibres (sphincter- 

 like) which are continued, as already referred to, to a considerable 

 distance along the trunks of the veins, retaining in this latter situa- 

 tion just the same character as at the auricle itself. This is a good 

 situation for seeing the branching and anastomosis of the fibres. 



Nutrition of the Heart. The heart is nourished by blood derived 

 from the aorta. Its arteries, the right and left coronary arteries, 

 are the first branches which spring from the aorta. They leave 

 that vessel just beyond the margins of the semilunar valves. The 

 right passes along the circular groove between the auricles and 

 ventricles, and sends a branch down the posterior median groove to 

 the apex ; the left passes along the anterior median groove, ana- 

 stomosing at the apex with the latter branches. Corresponding 

 with the small size and the oblique direction of the heart's fibres 

 are an extreme closeness and an everywhere oblique sloping of the 

 capillary network From this, venous radicles are formed at various 

 points and unite into large veins, which are found in the grooves 

 of the heart accompanying the arteries ; these veins terminate in 

 the coronary vein, which is lodged in the right portion of the 

 circular groove, and opens into the right auricle close to the orifice 

 of the inferior vena cava. 



Nerves. The nerves of the heart are derived from the cardiac 

 branches of the pneumogastric nerve, and from the sympathetic. 



