The Sternocleidomastoideus (Sternomastoid muscle) passes obliquely across the side of the neck and it acts to flex and rotate the head. It also acts as an accessory muscle of inspiration along with scalene muscles of the neck. The Sternocleidomastoideus varies much in the extent of its origin from the clavicle: in some cases the clavicular head may be as narrow as the sternal; in others it may be as much as 7.5 cm. in breadth. When the clavicular origin is broad, it is occasionally subdivided into several slips, separated by narrow intervals.