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5. The Fasciæ and Muscles of the Anterolateral Region of the Neck. a. The Superficial Cervical Muscle
The antero-lateral muscles of the neck may be arranged into the following groups: I. Superficial Cervical. III. Supra- and Infrahyoid. II. Lateral Cervical. IV. Anterior Vertebral. V. Lateral Vertebral. The Superficial Cervical Muscle
Platysma.
The Superficial Fascia of the neck is a thin lamina investing the Platysma, and is hardly demonstrable as a separate membrane.The Platysma (Fig. 378) is a broad sheet arising from the fascia covering the upper parts of the Pectoralis major and Deltoideus; its fibers cross the clavicle, and proceed obliquely upward and medialward along the side of the neck. The anterior fibers interlace, below and behind the symphysis menti, with the fibers of the muscle of the opposite side; the posterior fibers cross the mandible, some being inserted into the bone below the oblique line, others into the skin and subcutaneous tissue of the lower part of the face, many of these fibers blending with the muscles about the angle and lower part of the mouth. Sometimes fibers can be traced to the Zygomaticus, or to the margin of the Orbicularis oculi. Beneath the Platysma, the external jugular vein descends from the angle of the mandible to the clavicle. Variations occur in the extension over the face and over the clavicle and shoulder; it may be absent or interdigitate with the muscle of the opposite side in front of the neck; attachment to clavicle, mastoid process or occipital bone occurs. A more or less independent fasciculus, the Occipitalis minor, may extend from the fascia over the Trapezius to fascia over the insertion of the Sternocleidomastoideus. Nerve.—The Platysma is supplied by the cervical branch of the facial nerve. Actions.—When the entire Platysma is in action it produces a slight wrinkling of the surface of the skin of the neck in an oblique direction. Its anterior portion, the thickest part of the muscle, depresses the lower jaw; it also serves to draw down the lower lip and angle of the mouth in the expression of melancholy.
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