In human
Anatomy , the (pronounced ) '''muscles''' are muscles in the neck that act to flex and rotate the head.
It is given the name ''sternocleidomastoid'' because it attaches to the
Sternum (''sterno-''), the
Clavicle (''cleido-''), and the
Mastoid Process of the
Temporal Bone of the
Skull .
It is also called the .
The Sternocleidomastoideus (Sternomastoid muscle) passes obliquely across the side of the neck.
It is thick and narrow at its central part, but broader and thinner at either end. It arises from the
Sternum and
Clavicle by two heads.
- The or '''sternal head''' is a rounded Fasciculus , tendinous in front, fleshy behind, which arises from the upper part of the anterior surface of the Manubrium Sterni , and is directed upward, lateralward, and backward.
- The or '''clavicular head''', composed of fleshy and Aponeurotic fibers, arises from the superior border and anterior surface of the medial third of the Clavicle ; it is directed almost vertically upward.
The two heads are separated from one another at their origins by a triangular interval, but gradually blend, below the middle of the neck, into a thick, rounded muscle which is inserted, by a strong tendon, into the lateral surface of the
Mastoid Process , from its apex to its superior border, and by a thin
Aponeurosis into the lateral half of the
Superior Nuchal Line of the
Occipital Bone .
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.
More rarely, the adjoining margins of the Sternocleidomastoideus and
Trapezius have been found in contact.
The arises from the manubrium behind the Sternocleidomastoideus and passes behind the Sternocleidomastoideus to the upper surface of the clavicle.
