|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
| 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.
|5b. The Lateral Cervical Muscles|
| The lateral muscles are:|
|Trapezius and Sternocleidomastoideus.|
| The Trapezius is described on page 432.|
The Fascia Colli (deep cervical fascia) (Fig. 384).The fascia colli lies under cover of the Platysma, and invests the neck; it also forms sheaths for the carotid vessels, and for the structures situated in front of the vertebral column.
| The investing portion of the fascia is attached behind to the ligamentum nuchæ and to the spinous process of the seventh cervical vertebra. It forms a thin investment to the Trapezius, and at the anterior border of this muscle is continued forward as a rather loose areolar layer, covering the posterior triangle of the neck, to the posterior border of the Sternocleidomastoideus, where it begins to assume the appearance of a fascial membrane. Along the hinder edge of the Sternocleidomastoideus it divides to enclose the muscle, and at the anterior margin again forms a single lamella, which covers the anterior triangle of the neck, and reaches forward to the middle line, where it is continuous with the corresponding part from the opposite side of the neck. In the middle line of the neck it is attached to the symphysis menti and the body of the hyoid bone.|
| Above, the fascia is attached to the superior nuchal line of the occipital, to the mastoid process of the temporal, and to the whole length of the inferior border of the body of the mandible. Opposite the angle of the mandible the fascia is very strong, and binds the anterior edge of the Sternocleidomastoideus firmly to that bone. Between the mandible and the mastoid process it ensheathes the parotid glandthe layer which covers the gland extends upward under the name of the parotideomasseteric fascia and is fixed to the zygomatic arch. From the part which passes under the parotid gland a strong band extends upward to the styloid process, forming the stylomandibular ligament. Two other bands may be defined: the sphenomandibular (page 297) and the pterygospinous ligaments. The pterygospinous ligament stretches from the upper part of the posterior border of the lateral pterygoid plate to the spinous process of the sphenoid. It occasionally ossifies, and in such cases, between its upper border and the base of the skull, a foramen is formed which transmits the branches of the mandibular nerve to the muscles of mastication.|