External jugular vein

The external jugular vein receives the majority of venous blood from the exterior of the cranium, including the scalp, and the deep parts of the face. This vein is formed by the junction of the posterior division of the retromandibular vein with the posterior auricular vein. The external jugular vein drains into the subclavian vein lateral to or in front of the anterior scalene, piercing the roof of the posterior triangle.

Sensory branches of the cervical plexus

Branches of the cervical plexus emerge from the posterior triangle at the "nerve point" - a point which lies midway on the posterior border of the sternocleidomastoid. The sensory branches of the cervical plexus that are found in the space of the posterior triangle are listed below:

Greater auricular nerve (C2, C3) - innervates skin near the outer ear and the external acoustic meatus;
Transverse cervical nerve (C2, C3) - innervates the anterior region of the neck;
Supraclavicular nerves (C3, C4) - innervate skin above and below the clavicle;
Lesser occipital nerve (C2) - travels upward along the posterior edge of the sternocleidomastoid muscle, innervates skin of the posterior part of the auricle and skin of the lateral aspect of the back of the head.

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Content of the posterior triangle