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.

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

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.

Structure.—The origin of the muscle is fleshy, and as far as the middle of the neck it blends with its fellow. The common belly is then interrupted by a tendon, or sometimes two tendons, from which arise three or four fleshy bands. The lateral bands diverge to reach their insertion into the thyroid cartilage; while the inner bands, closely applied to each other and blending with the omo-hyoideus, pass straight forward to reach the ventral surface of the hyoid bone.

Relations.—At the root of the neck the common belly has the sterno-cephalicus below, and the carotid arteries and recurrent nerves above. Further forward the trachea becomes the upper relation, and near the head the skin and fascia, the lower one.

Blood-supply.—Carotid artery.

Nerve-supply.—Ventral branch of the first cervical nerve.

5. Omo-hyoideus (Subscapulo-hyoideus).—This is a thin, ribbon-like muscle, almost entirely fleshy, which crosses the trachea very obliquely under cover of the mastoido-humeralis.

Origin.—The subscapular fascia close to the shoulder joint.

Insertion.—The body of the hyoid bone, in common with the hyoid branch of the preceding muscle.

Action.—To depress the hyoid bone.

Structure.—The muscle is composed of parallel fleshy fibers, except at its origin, where it has a thin tendon.

Relations.—In the first part of its course the muscle passes forward between the supraspinatus, anterior deep pectoral, mastoido-humeralis (outwardly), and the scalenus (inwardly). It is intimately adherent to the mastoido-humeralis. In the middle of the neck it is related superficially to the mastoido-humeralis, sterno-cephalicus, and the jugular vein; deeply, to the rectus capitis anterior major, the carotid artery, the vagus, sympathetic, and recurrent nerves, the trachea, and, on the left side, the œsophagus. In its anterior part the muscle blends with the hyoid part of the sterno-thyro-hyoideus, the two covering the thyroid portion of the latter muscle, the thyroid gland, and the ventral face of the larynx.

Blood-supply.—Carotid and inferior cervical arteries.

Nerve-supply.—Ventral branches of the cervical nerves.

6. Scalenus (M. scalenus primæ costæ).—This muscle is deeply situated on the side of the posterior half of the neck. It is composed of two parts, between which the roots of the brachial plexus of nerves emerge.

Origin.—The anterior border and outer surface of the first rib.

Insertion.—(1) The dorsal (smaller) portion is attached to the transverse process of the seventh cervical vertebra; (2) the ventral portion is attached to the transverse processes of the sixth, fifth, and fourth cervical vertebræ.

Action.—The neck is flexed or inclined laterally, according as the muscles act together or singly. If the neck be the fixed point, the muscle may have a respiratory action by pulling forward or fixing the first rib.

Structure.—The dorsal portion is composed of three or four fleshy bundles. The ventral portion, which is much larger, is almost entirely fleshy, and not so divided.

Relations.—Superficially, the anterior deep pectoral, mastoido-humeralis, and omo-hyoideus muscles, the phrenic nerve, and the other branches of the brachial plexus; deeply, the vertebræ, the longus colli and intertransversales muscles, the œsophagus (on the left side), the trachea (on the right side), the vertebral vessels, the vagus, sympathetic, and recurrent nerves. The roots of the brachial plexus form a flat anastomosis, which lies between the two portions of the muscle. The brachial vessels cross the ventral edge close to the first rib.

Blood-supply.—Carotid, vertebral, and inferior cervical arteries.

Nerve-supply.—Ventral branches of the cervical nerves.

7. Rectus capitis anterior major (M. longus capitis).—This is the largest of the three special flexors of the head, and lies along the ventro-lateral surface of the anterior cervical vertebræ and the base of the cranium.

Origin.—The transverse processes of the fifth, fourth, and third cervical vertebræ.

Insertion.—The tubercles at the junction of the basilar process of the occipital bone with the body of the sphenoid.

Action.—Acting together, to flex the head; acting singly, to incline it to the same side also.

Structure.—The origin of the muscle is by fleshy digitations. The belly increases in size by the union of these digitations, reaching its maximum at the axis. It then diminishes, passes toward the median plane, and terminates on a rounded tendon.

Relations.—Superficially, the mastoido-humeralis, omo-hyoideus, and rectus capitis anticus minor, the submaxillary gland, the carotid artery (which lies along the lower border), the occipital and internal carotid arteries, and the tenth, eleventh, and sympathetic nerves; deeply, the vertebræ, the longus colli, intertransversales, and the small straight muscle. The terminal part of the muscle lies in contact with its fellow above the pharynx and between the guttural pouches.

Blood-supply.—Carotid, vertebral, and occipital arteries.

Nerve-supply.—Ventral branches of the cervical nerves.

8. Rectus capitis anterior minor (M. rectus capitis ventralis).—This is a small muscle which lies under cover of the preceding one.

Origin.—The ventral arch of the atlas.

Insertion.—The basilar process, close to the preceding muscle.

Action.—To flex the occipito-atlantal articulation.

Structure.—Fleshy.

Relations.—Below, to the preceding muscle; above, to the atlas, occipito-atlantal articulation, and the basilar process; externally, to the rectus capitis lateralis and the guttural pouch.

Blood-supply.—Occipital artery.

Nerve-supply.—Ventral branch of the first cervical nerve.

9. Rectus capitis lateralis.—This is a still smaller, entirely fleshy muscle, which lies for the most part under the small oblique muscle.

Origin.—The atlas, external to the preceding muscle.

Insertion.—The paramastoid or styloid process of the occipital bone.

Action.—The same as the preceding muscle.

Structure.—Fleshy.

Relations.—Superficially, the small oblique muscle, the occipital vessels, and the ventral branch of the first cervical nerve.

Blood-supply.—Occipital artery.

Nerve-supply.—Ventral branch of the first cervical nerve.

10. Longus colli.—This muscle covers the ventral surface of the vertebræ, from the sixth thoracic to the atlas, and is united with its fellow. It consists of two portions, thoracic and cervical.

Origin.—(1) Thoracic portion, the bodies of the first six thoracic vertebræ; (2) cervical portion, the transverse processes of the cervical vertebræ.

Insertion.—(1) Thoracic portion, the bodies and transverse processes of the last two cervical vertebræ; (2) cervical portion, the bodies of the cervical vertebræ and the tubercle on the ventral surface of the atlas.

Action.—To flex the neck.

Structure.—The muscle is composed of a succession of bundles. The largest of these constitute the thoracic part of the muscle, which has a strong tendon inserted into the last two cervical vertebræ. A bursa is interposed between the tendon and the spine at the first costo-vertebral articulation. The cervical portion consists of a number of smaller bundles, each of which passes from its origin on the transverse process of one vertebra forward and inward to its insertion into a vertebra further forward. The most anterior bundle is inserted by a strong tendon into the ventral tubercle of the atlas.

Relations.—The principal relations of the two muscles in the thorax are: ventrally, the pleura, and, further forward, the trachea and œsophagus; dorsally, the vertebræ and the costo-vertebral joints; laterally, the dorsal, superior cervical, and vertebral vessels, the sympathetic nerve, and the thoracic roots of the brachial plexus. In the neck, important relations are: ventrally, the trachea and œsophagus, the carotid artery, the vagus, sympathetic and recurrent nerves; dorsally, the vertebræ and, in the middle third of the neck, the intertransversales muscles; laterally, the scalenus, the rectus capitis anticus major, and the intertransversales (in the anterior third). The terminal part of the muscle is separated from the trachea by the œsophagus, which is here median in position.

Blood-supply.—Subcostal and vertebral arteries.

Nerve-supply.—Ventral branches of the spinal nerves.

11. Intertransversales colli (Mm. intertransversarii cervicis).—These are six fasciculi which occupy the spaces between the lateral aspects of the vertebræ and the transverse and articular processes. There is thus a bundle for each intervertebral articulation except the first. Each bundle consists of a dorsal and ventral portion.

Attachments.—The dorsal bundles pass from transverse process to articular process; the ventral bundles extend between adjacent transverse processes.

Action.—To bend the neck laterally.

Structure.—They contain strong tendinous intersections.

Relations.—Superficially, the mastoido-humeralis, rectus capitis anterior major, complexus, trachelo-mastoideus, splenius, scalenus, and longissimus muscles; deeply, the vertebræ, the longus colli muscle, and the vertebral vessels. The muscles are perforated by branches of these vessels and by the primary branches of the cervical nerves.

Blood-supply.—Vertebral artery.

Nerve-supply.—The cervical nerves.