The tenth cranial nerve (CN 10).
The vagus originates in the brainstem, travels through the subarachnoid (spinal fluid filled) space around the brain into a tunnel in base of the skull then out into the neck and down through the chest to the heart. Any process (tumor, infection, pressure from an overlying artery, etc.) could potentially irritate the vagus anywhere from where it originates to where it ends on the heart.
Important component of the autonomic nervous system. Controls heart rate, intestinal movement, gastric acid secretion, etc.
Recurrent laryngeal nerve: a branch of the vagus nerve that supplies the vocal cord. Liable to injury during anterior cervical discectomy.