ABSTRACT
Trapezius (1), supplied by the accessory nerve (2), extends the neck, shrugs the shoulders, and helps scapular rotation during abduction of the upper limb. Sternocleidomastoid (3) (accessory nerve) is a prominent feature of the lateral neck. It is related superficially to the external jugular vein (4) and deeply to the internal jugular vein (5) in the carotid neurovascular bundle. The muscle arises by sternal (7) and clavicular (8) heads from the manubrium and from the medial part of the clav icle. These two heads and the intervening fossa may be clearly visible. Sternocleidomastoid attaches to the mastoid process and superior nuchal line on the skull. Acting alone, it laterally flexes the neck to tilt the ear to the ipsilateral shoulder. But it rotates the face in the opposite direction. Such a position (wry neck) may be seen following injury to sternocleido mastoid, or to its nerve supply. Acting together (and with other neck muscles) the two sternocleido mastoids extend the head on the flexed neck, e.g. when straining to look over the heads of a crowd.
