THE CARDIAC NERVES. 473 



viz., the cardiac nerves of the sympathetic in the neck, the cardiac 

 branches of the trunk of the vagus in both the neck and chest, and 

 the cardiac offsets of the recurrent branch. 



The branches of this half of the plexus are distributed mostly to branches to 

 the right side of the heart, and pass downwards before and behind 

 the right branch of the pulmonary artery ; those in front run on the 

 trunk of the pulmonary artery to end in the right coronary plexus 

 (p. 457) ; and the nerves behind supply the right auricle of the 

 heart. Offsets are sent laterally on the branch of the artery to the 

 root of the lung. rooTo 



The left half of the plexus lies close to the ligament of the arterial Left part : 

 duct, and rather on the left of the trachea. In it are collected the enterin<*it- 

 cardiac nerves of the sympathetic ganglia of the left side of the 

 neck, except the highest, and numerous and large branches of 

 the left recurrent nerve of the vagus. 



Nerves descend from it to the heart around the left branch and offsets end 

 the trunk of the pulmonary artery, and after supplying branches to 

 the left auricle, terminate in the left coronary plexus (p. 457). 

 A considerable offset is directed forwards by the side of the ligament 

 to the superficial cardiac plexus ; and some nerves reach the left and in root 

 anterior pulmonary plexus by coursing along the branch of the of lung> 

 pulmonary artery. 



Termination of the three cardiac branches of the sympathetic nerve other car- 

 of the neck (upper, middle, and lower). 



On the right side there may be only two cardiac nerves entering The right 

 the thorax, for the highest nerve is often blended with one of 

 the others. These nerves pass beneath the subclavian artery to the 

 right half of the deep plexus ; and they communicate with the 

 branches of the recurrent laryngeal nerve of the vagus. 



On the left side the highesjt cardiac nerve lies over the arch of the One left 

 aorta, and ends in the superficial cardiac plexus ; it may give a superficial 

 branch beneath the arch to the deep plexus. Only one other nerve, a11 others 

 the middle cardiac, is usually seen entering the left side of the deep plexus, 

 plexus, as the lower one generally blends with it. 



OPENING OF THE AORTA AND STRUCTURE OF THE HEART. 



Dissection. The aorta having been cut across, the student will 

 examine its interior as it springs from the heart. 



The opening of the aorta is anterior to that of the auricle, and Aortic open- 

 close to the septum. This aperture is round, and rather smaller mg " 

 than that of the pulmonary artery, measuring slightly less than an size and 

 inch in diameter. position; 



In its interior is a valve of three semilunar or sigmoid flaps, valve, 

 which are thicker and stronger than the corresponding parts in the 

 pulmonary artery, but have a like structure and attachment (p. 461). 

 The projection in the centre of each valve, the coi-pus Arantii, is 

 better marked. Opposite each valve the coat of the aorta is bulged 

 as in the pulmonary artery, though in a greater degree, and forms 



