Part 63

Structure.—Fleshy, composed of parallel transverse bundles.

Blood-supply.—Lingual artery.

Nerve-supply.—Glosso-pharyngeal nerve.

7. =Sterno-thyro-hyoideus=, and

8. =Omo-hyoideus.=—These are described with the muscles on the ventral surface of the neck.

THE FASCIÆ AND MUSCLES OF THE NECK

It is convenient to divide the muscles of the neck into ventral and lateral groups, the two lateral groups being separated from each other by the ligamentum nuchæ.

THE FASCIÆ OF THE NECK

The =superficial fascia= is in part two-layered, and contains the cervical portion of the panniculus. The fasciæ of the right and left sides are attached along the dorsal line of the neck to the ligamentum nuchæ, while along the ventral line they meet in a fibrous raphé. A deep layer is detached which passes underneath the panniculus, bridges over the jugular furrow, and crosses over the deep face of the mastoido-humeralis and omo-hyoideus to join the superficial layer. It again separates to pass under the cervical trapezius, and become attached to the ligamentum nuchæ. Along the ventral line a septum is detached which separates the sterno-cephalici. Two other layers in front of the shoulder inclose the prescapular lymph glands.

The =deep fascia= also forms two layers. The =superficial layer= is attached to the wing of the atlas and the lower edge of the trachelo-mastoideus and scalenus. Passing downward, it incloses the trachea, and, together with the deep layer, furnishes sheaths for the vagus and sympathetic nerves and the carotid artery. Passing upward it detaches septa between the extensor muscles of the spine. Anteriorly it covers the thyroid gland, the guttural pouch, the adjacent vessels and nerves and the larynx, and is attached to the mastoid process of the temporal bone and the thyroid cornu of the hyoid bone. Posteriorly, it is attached to the first rib and the cariniform cartilage of the sternum. The =deep layer= (prevertebral fascia) covers the ventral surface of the longus colli, and incloses the trachea and œsophagus. Anteriorly, it forms, with the corresponding layer of the opposite side, a septum between the guttural pouches; posteriorly, it becomes continuous with the endothoracic fascia. A =fascia propria= forms a tubular sheath around the trachea, inclosing also the recurrent nerves.

VENTRAL MUSCLES

This group consists of eleven pairs of muscles which lie almost entirely ventral to the vertebræ.

1. =Panniculus carnosus.=—The =cervical panniculus= (platysma myoides of man) has a fleshy origin on the cariniform cartilage (manubrium) of the sternum. it passes forward, outward, and upward, crossing over the sterno-cephalicus and jugular furrow obliquely. On reaching the surface of the mastoido-humeralis it adheres closely to this muscle, and soon thins out, to be continued over the splenius and trapezius by an aponeurosis which is difficult to remove from the latter muscle. Scattered bundles may be traced on the ventral surface of the neck to the facial portion. The right and left muscles meet at a ventral median raphé in pennate fashion.

FIG. 177.—ANTERO-LATERAL VIEW OF MUSCLES AND SKELETON OF HORSE.

a, Trapezius; c, mastoido-humeralis; d, sterno-cephalicus; f, long head of triceps; f′, external head of triceps; g, anterior superficial pectoral muscle; g′, posterior superficial pectoral; h′, anterior deep pectoral; v, cervical panniculus; z, supraspinatus; 29, omo-hyoideus; 30, sterno-thyro-hyoideus; 31, jugular vein; 32, cephalic vein; 1, scapula; 1′, cartilage of scapula; 2, spine of scapula; 4, shaft of humerus; 4′, external epicondyle; 5, external tuberosity of humerus; 6, deltoid tuberosity; 14, ventral border (“keel”) of sternum; 14′, cariniform cartilage; l.R., first rib. (After Ellenberger-Baum, Anat. für Künstler.) ]

2. =Mastoido-humeralis.=—This is described on p. 252.

3. =Sterno-cephalicus= (Sterno-maxillaris s.-mandibularis).—This is a long, narrow muscle, extending along the ventral and lateral aspects of the trachea from the sternum to the angle of the jaw. It forms the ventral boundary of the jugular furrow.

Origin.—The cariniform cartilage of the sternum.

Insertion.—The posterior border of the lower jaw.

Action.—Acting together, to flex the head and neck; acting singly, to incline the head and neck to the side of the muscle contracting.

Structure.—The two muscles are fused at their origin, which is fleshy. Near the middle of the neck they separate, and, becoming thinner, each muscle passes under the parotid gland and terminates in a flat tendon.

Relations.—Superficially, the cervical panniculus; deeply, the sterno-thyro-hyoideus and omo-hyoideus muscles. The upper edge of the muscle is related to the jugular vein, which lies in the jugular furrow. The carotid artery, the vagus, sympathetic, and recurrent nerves also lie along the upper edge at the root of the neck. The tendon passes under the submaxillary vein and the parotid gland, having the submaxillary gland and stylo-maxillaris muscle on its inner side.

Blood-supply.—Carotid artery.

Nerve-supply.—Ventral branches of the spinal accessory and first cervical nerves.

4. =Sterno-thyro-hyoideus= (Sterno-thyroideus et sterno-hyoideus).—This is a long, slender, digastric muscle, applied to the ventral surface of the trachea and its fellow of the opposite side.

Origin.—The cariniform cartilage of the sternum.

Insertion.—(1) The external surface of the thyroid cartilage of the larynx; (2) the body of the hyoid bone.

Action.—To depress and retract the hyoid bone, the base of the tongue, and the larynx, as in deglutition. It may also fix the hyoid bone when the depressors of the tongue are acting, as in suction.