On the right side it descends posterior to the common carotid artery, and at the root of the neck runs either anterior or posterior to the subclavian artery; it then descends upon the trachea, receives a few filaments from the recurrent nerve, finally joining the right half of the deep cardiac plexus.
On the left side, the middle cardiac nerve enters the chest between the left carotid and the left subclavian artery, and joins the left half of the deep part of the cardiac plexus.
