CARDIAC. 667 



side of the superior intercostal artery. Its form is irregular; it is larger in 

 size than the preceding, and frequently joined with the first thoracic ganglion. 



Its superior branches communicate with the middle cervical ganglion. 



Its inferior branches descend, some in front of, others behind the subclavian 

 artery, to join the first thoracic ganglion. The most important of these branches 

 constitutes the inferior cardiac nerve, to be presently described. 



The external branches consist of several filaments, some of which communicate 

 with the seventh and eighth spinal nerves ; others acco.mpany the vertebral 

 artery along the vertebral canal, forming a plexus round the vessel, supplying 

 it with filaments, and communicating with the cervical spinal nerves as high 

 as the fourth. 



CARDIAC NERVES. 



The Cardiac Nerves are three in number on each side ; superior, middle, and 

 inferior, one being derived from each of the cervical ganglia. 



The superior cardiac, nerve (nervus superficialis cordis) arises by two or more 

 branches from the superior cervical ganglion, and occasionally receives a fila- 

 ment from the cord of communication between the first and second cervical 

 ganglia. It runs down the neck behind the common carotid artery, lying upon 

 the Longus Colli muscle ; and crosses in front of the inferior thyroid artery, 

 and the recurrent laryngeal nerve. 



The right superior cardiac nerve, at the root of the neck, passes either in front 

 of or behind the subclavian artery, and along the arteria innorninata, to the 

 back part of the arch of the aorta, where it joins the deep cardiac plexus. This 

 nerve, in its course, is connected with other branches of the sympathetic ; about 

 the middle of the neck it receives filaments from the external laryngeal nerve; 

 lower down, one or two twigs from the pneumogastric ; and as it enters the 

 thorax, it joins with the recurrent laryngeal. Filaments from this nerve accom- 

 pany the inferior thyroid artery to the thyroid gland. 



The left superior cardiac nerve runs by the side of the left carotid artery, and 

 in front of the arch of the aorta, to the superficial cardiac plexus ; but occa- 

 sionally it passes behind the aorta, and terminates in the deep cardiac plexus. 



The middle cardiac nerve (nervus cardiacus magnus), the largest of the three, 

 arises from the middle cervical ganglion, or from the cord between the middle 

 and inferior ganglia. On the right side, it descends behind the common carotid 

 artery ; and, at the root of the neck, passes either in front of or behind the sub- 

 clavian artery ; it then descends on the trachea, receives a few filaments from 

 the recurrent laryngeal nerve, and joins the deep cardiac plexus. In the neck, 

 it communicates with the superior cardiac and recurrent laryngeal nerves. On 

 the left side, the middle cardiac nerve enters the chest between the left carotid 

 and subclavian arteries, and joins the left side of the deep cardiac plexus. 



The inferior cardiac nerve (nervus cardiacus minor) arises from the inferior 

 cervical or first thoracic ganglion. It passes down behind the subclavian artery, 

 and along the front of the trachea, to join the deep cardiac plexus. It commu- 

 nicates freely behind the subclavian artery with the recurrent laryngeal and 

 middle cardiac nerves. 



The great or deep cardiac plexus (plexus magnus profundus Scarpa) is situated 

 in front of the trachea at its bifurcation, above the point of division of the pul- 

 monary artery, and behind the arch of the aorta. It is formed by the cardiac 

 nerves derived from the cervical ganglia of the sympathetic, and the cardiac 

 branches of the recurrent laryngeal and pneumogastric. The only cardiac 

 nerves which do not enter into the formation of this plexus, are the left supe- 

 rior cardiac nerve, and the left inferior cardiac branch from the pneumogastric. 

 The branches derived from the great cardiac plexus form the posterior coronary 

 plexus, and part of the anterior coronary plexus ; whilst a few filaments pro- 

 ceed to the pulmonary plexuses, and to the auricles of the heart. 



