. Applied anatomy and kinesiology. g. 132shows how it is protruded when the diaphragm contracts in taking a full breath. STERNOCLEIDOMASTOID. A pair of muscles forming a letter V down the front and sides ofthe neck. Origin.—The mastoid process of the skull. SCALENI 217 Insertion.^—The front of the sternum aiul the inner third of theposterior border of the chivicle. Structure.—Parallel fibers, dividing into two parts below its middle. Action.—As a breathing muscle, it lifts the sternum, bothmuscles of the pair acting together, while the head is held rigidlyupright. When the lower end is the fix
. Applied anatomy and kinesiology. g. 132shows how it is protruded when the diaphragm contracts in taking a full breath. STERNOCLEIDOMASTOID. A pair of muscles forming a letter V down the front and sides ofthe neck. Origin.—The mastoid process of the skull. SCALENI 217 Insertion.^—The front of the sternum aiul the inner third of theposterior border of the chivicle. Structure.—Parallel fibers, dividing into two parts below its middle. Action.—As a breathing muscle, it lifts the sternum, bothmuscles of the pair acting together, while the head is held rigidlyupright. When the lower end is the fixed point, which is moreusual, one of the pair rotates the face to the opposite side and thetwo flex the neck. The sternocleidomastoid is an important muscle of respiration,acting in labored breathing in such exercises as running or in makinga deep inhalation for any purpose. It is able to assist greatly incases where some of the other muscles of breathing are lost. The lower portion of this muscle is shown well in Fig. Fig. 133.—The scaleni. (Gray.) SCALENI. Three muscles named the anterior, middle, and posterior scalenifrom their relative positions and their triangular form as a grouj)(Fig. 133). 218 BREATHING Origin.—The transverse processes of the cervical vertebrae. Insertion.—^The anterior and middle scaleni, on the upper sur-face of the first rib; the posterior on the second rib. Structure.—Longitudinal fibers, tendinous at each end. Action.—The scaleni are in a position to support the upper ribswhen the intercostals contract and to lift them by strong contrac-tion, providing the neck is held firmly erect. The presence of thebrachial plexus of nerves makes it difficult to secure satisfactoryisolated action of the scaleni, but under the mild stimulus that canbe given them, the elevation of the first ribs and sternum has beenseen. The inability of the scaleni to sustain and lift the chest whenthe neck is not held up is the most serious result of mild
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