314 DISSECTION OF THE THORAX. 



artery, and is directed onwards in the depression between the right auricle 

 and ventricle to end in the left half of the heart on the posterior aspect. 

 In its course branches are distributed upwards and downwards to the right 

 half of the viscus. Two of these are of larger size than the rest : one runs 

 on the anterior aspect of the right ventricle towards the free margin ; the 

 other descends on the back of the heart towards the apex, along the septum 

 between the ventricles. 



The left corewary branch is inclined behind the pulmonary artery to the 

 left side of that vessel, and in the groove between the left auricle and ven- 

 tricle to the back of the same side of the heart. Like the preceding artery, 

 it furnishes offsets to the substance of the auricle and ventricle of its side : 

 the largest of these descends in the anterior sulcus over the septum ven- 

 triculorum towards the apex. 



The veins of the substance of the heart (cardiac) are not the same in 

 number, nor have they the same arrangement as the arteries. There may 

 be said to be three sets, but for the most part they are collected into one 

 large trunk, the coronary sinus, which opens into the right auricle. 



The coronary sinus (fig. 99, *) will be seen on raising the heart to be 

 placed in the sulcus between the left auricle and ventricle. About an inch 

 usually in extent, it is joined at the one end by the great coronary vein ( 4 ) ; 

 and at the other it opens into the right auricle. It is crossed by the mus- 

 cular fibres of the left auricle. Inferiorly and at its right end it receives 

 some branches from the back of the ventricles ( 3 and |) ; and nearly at 

 its left extremity another vein ( 2 ), the oblique vein (Marshall), which 

 ascends along the back of the left auricle. 



On slitting the sinus with a scissors the openings of its different veins 

 will be seen to be guarded with valves, with the exception of the oblique 

 vein ; and at its right end is the large Thebesian valve of the right auricle. 



The great cardiac or coronary vein begins in front near the apex of the 

 heart, in the substance of the ventricles. The vessel turns to the posterior 

 surface in the sulcus between the left auricle and ventricle, and opens into 

 the coronary sinus (fig. 99, 4 ). It receives collateral branches in its course, 

 and its ending in the sinus is marked by two valves. 



Anterior and posterior cardiac veins. Some small veins on the ante- 

 rior part of the right ventricle open separately, by one or more trunks, 

 into the lower part of the right auricle. Similar small veins exist over 

 the back of the ventricles ; and one, larger than the rest, lies over the 

 septum ventriculorum : they enter the coronary sinus by separate valved 

 openings. 



Smallest cardiac. A third set of veins (venre minima?) lie in the sub- 

 stance of the heart, and are noticed in the description of the right auricle. 



Cardiac nerves. The nerves for the supply of the heart are derived from 

 a large plexus (cardiac) around the roots of the aorta, and pulmonary artery. 

 Part of this plexus is superficial to the pulmonary artery, and part beneath ; 

 and an offset is sent from eacli with a coronary artery. Only the superfi- 

 cial part of the plexus can now be seen. 



The superficial cardiac plexus is placed below the arch of the aorta, 

 and by the side of the ductus arteriosus. The nerves joining it are the 

 left superficial cardiac of the sympathetic, the lower cardiac of the left 

 vagus (p. 331), and a considerable bundle from the deep cardiac plexus. 

 A small ganglion is sometimes seen in the plexus. Inferiorly it sends off 

 nerves on the right coronary artery to the heart. A few filaments pass on 

 the left division of the pulmonary artery to the left lung. 



