Anterolateral Region

The anterolateral muscles of the neck may be arranged into the following groups;

1. Superficial and lateral cervical
2. Supra- and infra-hyoid
3. Anterior vertebral
4. Lateral vertebral

The superficial fascia of the neck is a thin lamina investing the Platysma and is hardly demonstrable as a separate membrane.

The deep cervical fascia (fig. 588) lies under cover of the Platysma, and invests the muscles of the neck. It consists of fibro-areolar tissue, which occupies all the intervals that would otherwise exist between the muscles, viscera, vessels, etc, of the neck. In certain situations the white fibers predominate, and the fascia assumes the form of a thin fibrous sheet or layer, but elsewhere the tissue is loosely arranged and is easily broken down. It becomes condensed around the blood-vessels, providing them with fibrous sheaths which here, as elsewhere in the body, bind the arteries and their accompanying veins closely together.

The investing portion of the fascia is attached behind to the ligamentum nuchae and to the spine of the seventh cervical vertebra. It forms a thin investment for the Trapezius, and from the anterior border of this muscle is continued forwards, as a rather loose areolar layer covering the posterior triangle of the neck, to the posterior border of the Sternocleidomastoid, where it begins to assume the appearance of a fascial membrane. Along the hinder edge of the Sternocleidomastoid 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 forwards to the median plane, where it is continuous with the corresponding lamella from the opposite side of the neck. In the median plane of the neck it is fixed to the symphysis menti and the body of the hyoid bone.

Figure 588
Above, the fascia is attached to the superior nuchal line of the occipital bone, to the mastoid process of the temporal bone, and to the whole length of the base of the mandible. Opposite the angle of the mandible it is very strong, and hinds the anterior edge of the Sternocleidomastoid firmly to that bone. Between the mandible and the mastoid process it ensheathes the parotid gland-the layer which covers the gland extends upwards under the name of the parotid fascia and is fixed to the zygomatic arch. From the part which passes deep to the parotid gland a strong band ascends to the styloid process, forming the stylomandibular ligament.

Below, the fascia is attached to the acromion, the clavicle and the manubrium sterni. Some little distance above the last, it splits into a superficial and a deep layer. The former is attached to the anterior border of the manubrium, the latter to its posterior border and to the interclavicular ligament. Between these two layers there is a slit-like interval, termed the suprasternal space; it contains a small quantity of areolar tissue, the lower portions of the anterior jugular veins and the jugular arch, the sternal kneads of the Sternocleidomastoid muscles, and sometimes a lymph-gland.

The carotid sheath is a condensation of the cervical fascia in which the common and internal carotid arteries, the internal jugular vein, the vagus nerve and the constituents of the ansa hypoglossi are imbedded. It is thicker on the arteries than it is on the vein, and peripherally it is connected to the neighboring layers by loose areolar tissue (fig. 589).

Figure 589
The Prevertebral layer of the cervical fascia covers the prevertebral muscles and extends laterally on the Scalenus anterior, the Scalenus medius and the Levator scapulae muscles, i.e. it forms a fascial floor for the posterior triangle of the neck. As the subclavian artery and the brachial nerves emerge from behind the Scalenus anterior they carry the Prevertebral fascia downwards and laterally behind the clavicle to form the axillary sheath. Traced laterally round the neck, the prevertebral fascia, rapidly becomes thinner and more areolar in character and it is lost as a definite fibrous layer under cover of the Trapezius. Superiorly it is attached to the base of the skull, and inferiorly it is carried downwards in front of the longus cervicis (longus colli) muscles into the superior mediastinum, where it blends with the anterior longitudinal ligament. Anteriorly the Prevertebral layer is separated from the pharynx and its covering buccopharyngeal fascia by a loose cellular interval, which is termed the retropharyngeal space. Further from the median plane, the same loose areolar tissue connects the prevertebral layer to the pretracheal fascia, the carotid sheath and the fascia on the deep surface of the Sternocleidomastoid muscle. It should be observed that all the anterior primary rami of the cervical nerves lie at first on the deep aspect of the prevertebral layer, and certain of their important branches retain this position throughout their course in the neck, viz. the phrenic, the nerve to the Rhomboids (dorsalis scapulae nerve) and the nerve to Serratus anterior (long thoracic).

The pretracheal layer of the cervical fascia is very thin and owes such importance as it possesses to its intimate relationship with the thyroid gland, for which it provides a fine fascia] sheath. Above, it is attached to the arch of the cricoid cartilage, and below it is continued into the superior mediastinum, is an investment for the inferior thyroid veins.

Applied Anatomy.-The deep cervical fascia is of considerable importance from a surgical point of view. The investing layer opposes the extension of abscesses towards the surface and pus forming beneath it has a tendency to extend laterally. If the pus be contained in the anterior triangle, it may find its way into the mediastinum, in front of the pretracheal layer of fascia; but owing to the thinness of the fascia in this situation it more frequently finds its way to the surface and points above the sternum. Pus forming behind the prevertebral layer, in cases, for instance, of caries of the bodies of the cervical vertebrae, may extend towards the lateral part of the neck and point in the posterior triangle, or may perforate this layer of fascia and the buccopharyngeal fascia and point into the pharynx (retropharyngeal abscess).

In cases of cut throat, when the wound involves only the investing layer the injury is usually trivial, the special danger being injury to the external jugular vein. But where the second of the two layers is opened up, important structures may be injured, and serious results follow.

 

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