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 By TeachMeSeries Ltd (2025) Fig 1- Lateral view of the neck. Note the two heads of the sternocleidomastoid Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Pro Feature - Dissection Images Superficial dissection of the neck, demonstrating the platysma and underlying structures. Superficial dissection of the neck, demonstrating the platysma and underlying structures. You've Discovered a Pro Feature Access our Dissection Image Library Enhance your understanding with high-resolution dissection images showcasing real-life anatomy. Learn More Print Article Rate This Article