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184 ANAT03IY.

and when these parts are fixed it dra^s the angle of the mouth down-
ward and outward. The muscle is brought into use in the act of
deglutition, and also acts during sudden fright.
The Stcnio-cleido-mastoideus (Fig. 94) is a long, strong muscle, extend-
ing obliquely across the neck, from the mastoid process of the temporal
bone to the sternum and clavicle. It divides the surgical square of the
neck into two great triangles, anterior and posterior, and is ensheathed
Fig. 94.

Muscles of the Neck, anterior view.
by two layers of the deep cervical fascia. It arises by two heads, the
sternal and the clavicular.
The Sternal Head is thick and rounded, tendinous in front, fleshy
behind, arising from the superior and outer part of the manubrium of
the sternum.
The Clavicular Head is flat, and is composed of fleshy and tendinous
fibres; arising from the inner third of tlie superior border of the clavicle,
it passes ahnost directly upward. The triangular space between the
two heads is filled up by areolar tissue. The two divisions gradually
unite midway in the neck, forming a thick round prominent muscle,
which extends u])\vard and backward, and is in.serted by short and
strong tendinous fibres into the external surface of the mastoid process,
commencing at its apex and extending upward and backward along the
superior curved line of the occipital bone, or semicircular line of the