sternocleidomastoids
The sternocleidomastoids, also known as the sternocleidomastoid muscles, are paired muscles of the anterior and lateral neck. Each muscle has two heads: a sternal head arising from the manubrium and a clavicular head arising from the medial third of the clavicle. The fibers converge to insert on the mastoid process of the temporal bone and the adjacent superior nuchal line. They are prominent landmarks in neck anatomy and can act as accessory muscles of respiration in severe breathing effort.
Innervation and blood supply: The sternocleidomastoids are innervated primarily by the spinal accessory nerve (cranial nerve
Actions: Unilateral contraction of a sternocleidomastoid rotates the head to the opposite side and laterally flexes
Clinical relevance and variation: Variants include dual heads or accessory slips. Clinically, the sternocleidomastoids can be