Click image to view full screen

Identify the largest cutaneous nerve of the cervical plexus, the great auricular nerve (C2,C3). It crosses the surface of the superior part of the sternocleidomastoid muscle and lies adjacent to the external jugular vein. Usually, at the level of the angle of mandible, the great auricular nerve divides into two branches. The anterior branch innervates the skin over the angle of the mandible, and the posterior branch innervates the skin immediately inferior to the ear.

Links and References:
Grant's: 8.4
Netter:172