The Posterior Triangle of the Neck

Knowledge of the neck anatomy is necessary to examine the musculoskeletal, nervous, respiratory, digestive, endocrine, lymphatic, and cardiovascular systems. After all, the neck is much more than a pedestal for the head. It has a lot going on inside.

The superficial structures of the neck include mostly muscles, blood vessels, and nerves that either work in the neck or travel through the neck to get to the head or the trunk. The superficial structures are located in two triangles: the anterior triangle of the neck, and the posterior triangle of the neck.

The sternocleidomastoid muscle (SCM) is visible on either side of the neck. It separates the posterior triangle of the neck from the anterior triangle of the neck. It’s attached to the sternum and clavicle and the mastoid process of the temporal bone of the skull.

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The sternocleidomastoid muscle has two portions (somewhat like two prongs): the sternal head and the clavicular head. The sternal head originates on the manubrium (the upper part of the sternum), and the clavicular head originates on the medial part of the clavicle. The space between the two heads is called the lesser supraclavicular fossa. The two heads join together as they move upward and insert onto the mastoid process of the temporal bone (the easily palpated bony bump located just behind and below the ear).

Contracting one sternocleidomastoid muscle tilts your head to that side and can rotate the head in the opposite direction. Contracting both at the same time flexes the neck and extends the head. The spinal accessory nerve (CN XI) provides the efferent (motor) innervation, and the afferent (sensory) innervation comes from the C3 and C4 spinal nerves.

The borders of the posterior triangle of the neck are formed by the trapezius muscle posteriorly, the sternocleidomastoid muscle anteriorly, and the omohyoid muscle inferiorly. The roof is formed by fascia, and the floor is formed by the splenius capitus, levator scapulae, and scalene muscles.

The posterior triangle of the neck is home to parts of several muscles:

  • Splenius capitis

  • Levator scapula

  • Anterior, middle, and posterior scalenes

You find several nerves in the posterior triangle of the neck, too:

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  • Spinal accessory nerve (cranial nerve XI)

  • Roots of the brachial plexus

  • Suprascapular nerve

  • Cutaneous branches of the cervical plexus:

    • Lesser occipital nerve

    • Great auricular nerve

    • Transverse cervical nerve

    • Supraclavicular nerve

  • Phrenic nerve

The posterior triangle of the neck has several veins and arteries:

  • External jugular vein

  • Subclavian vein

  • Brachiocephalic vein

  • Cervicodorsal vein

  • Suprascapular artery

  • Occipital artery

  • Part of the subclavian artery

The borders of the posterior triangle of the neck are formed by the trapezius muscle posteriorly, the sternocleidomastoid muscle anteriorly, and the omohyoid muscle inferiorly. The roof is formed by fascia, and the floor is formed by the splenius capitus, levator scapulae, and scalene muscles.

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