Sternocleidomastoid

The sternocleidomastoid is a muscle of the anterolateral aspect of the neck.

Attachments:
- Sternal head originates from the manubrium of the sternum
- Clavicular head originates from the medial third of the clavicle
- Both heads attach to the mastoid process of the temporal bone and the superior nuchal line of the occipital bone.
Actions: Lateral flexion and rotation of the neck when acting unilaterally, and extension of the neck at the atlanto-occipital joints when acting bilaterally.
Innervation: Accessory nerve
Blood supply:
- Upper third – Occipital artery
- Middle third – Superior thyroid artery and external carotid artery
- Lower third – Suprascapular artery