The posterior auricular vein begins upon the side of the head, in a plexus

Plexus

A plexus is a part of nervous system. Plexus has a slightly different definition in vertebrates and in invertebrates.- In vertebrates :In vertebrates, a plexus is an area where nerves branch and rejoin. The electrical signals do not mix; rather, the fibres travel together with their electrical...

 which communicates with the tributaries of the occipital vein

Occipital vein

The occipital vein begins as a plexus at the posterior aspect of the scalp from the external occipital protuberance and superior nuchal line to the back part of the vertex of the skull....

 and superficial temporal veins.

It descends behind the auricula, and joins the posterior division of the posterior facial vein

Posterior facial vein

The retromandibular vein , formed by the union of the superficial temporal and maxillary veins, descends in the substance of the parotid gland, superficial to the external carotid artery but beneath the facial nerve, between the ramus of the mandible and the sternocleidomastoideus muscle.It divides...

 to form the external jugular.

It receive the stylomastoid vein, and some tributaries from the cranial surface of the auricula.