The greater auricular nerve arises from the ventral rami of C2 and C3 and is the largest ascending branch of the cervical plexus.  It passes forwards around the posterior border of the sternocleidomastoid muscle and close to its midpoint pierces the deep cervical fascia to ascend on the surface of the muscle with the external jugular vein, deep to platysma.  On its journey to the parotid gland, on the surface of the sternocleidomastoid muscle, it divides into anterior and posterior branches.  

The anterior branch joins the facial nerve within the parotid gland and terminates in the facial skin overlying it.  The posterior branch terminates in the skin over and below the mastoid process, and the posterior aspect of the ear.  The posterior branch forms connections with the lesser occipital nerve, the auricular branch of the vagus nerve (X cranial nerve) and the posterior auricular branch of the facial nerve.

Supply
The greater auricular nerve supplies facial skin overlying the parotid gland and skin over and below the mastoid process, and the posterior aspect of the ear.