The Cardiac Nerves, derived from these sources, converge from both sides upon the origin of the aorta and pulmonary artery, and form the cardiac plexuses, which, dividing into the right and left coronary plexuses, surround and accompany the coronary arteries and their branches.

There are three principal cardiac nerves derived from the sympathetic on each side, viz., the superior or superficial cardiac, the middle or deep cardiac, and the inferior or small cardiac nerves.

The Superior Cardiac Nerve

The Superior Cardiac Nerve arises from the superior cervical ganglion of the sympathetic, or from the communicating branch which connects this ganglion with the middle; it is joined by one or two filaments from the pneumogastric nerve.

The Middle Cardiac Nerve

The Middle Cardiac Nerve arises from the middle cervical ganglion; but when this ganglion is absent, the nerve arises from the trunk of the sympathetic itself. Scarpa has called this the great cardiac nerve, from its frequently being the largest of the three: sometimes, however, it is absent altogether.