sternocleidomastoïdeus
The sternocleidomastoideus, commonly known as the sternocleidomastoid muscle, is a prominent paired muscle of the neck. It has two heads: a sternal head arising from the manubrium of the sternum and a clavicular head arising from the medial third of the clavicle. Both heads insert at the mastoid process of the temporal bone and the adjacent superior nuchal line. The muscle lies superficial to many deeper neck structures and helps define the contour of the neck. It forms part of the posterior border of the anterior and posterior triangles of the neck.
Anatomical relations include its position as a key landmark in the neck, separating the anterior from the
Functionally, contraction of the sternocleidomastoideus is bilateral or unilateral. Unilateral contraction rotates the head to face
Innervation is provided primarily by the spinal accessory nerve (cranial nerve XI), with proprioceptive input from