Part 67

Blood-supply.—Vertebral and superior cervical arteries.

Nerve-supply.—Dorsal branches of the last six cervical nerves.

6. =Complexus= (M. semispinalis capitis).—This is a large triangular muscle which lies chiefly on the ligamentum nuchæ, under cover of the splenius and trachelo-mastoideus muscles.

Origin.—(1) The second, third, and fourth thoracic spines, in common with the splenius and serratus anticus; (2) the transverse processes of the first six or seven thoracic vertebræ; (3) the articular processes of the cervical vertebræ.

Insertion.—The posterior surface of the occipital bone, external to the funicular portion of the ligamentum nuchæ.

Action.—It is the chief extensor of the head and neck. Acting singly, the muscle inclines the head to the same side.

Structure.—The origin of the muscle at the withers is aponeurotic. In the neck the bundles arising from the articular processes run obliquely upward and forward, giving the lower part of the muscle a distinct pennate character. The upper part of the belly is crossed obliquely by four or five tendinous intersections. The insertion is by a strong tendon.

Relations.—Superficially, the rhomboideus, serratus magnus, splenius, and trachelo-mastoideus muscles; deeply, the ligamentum nuchæ, the multifidus cervicis, longissimus, and the oblique and posterior straight muscles of the head, the deep or superior cervical vessels, and the dorsal cutaneous branches of the cervical nerves.

Blood-supply.—Deep cervical, vertebral, and occipital arteries.

Nerve-supply.—Dorsal branches of the last six cervical nerves.

7. =Multifidus cervicis= (M. semispinalis colli; transverse spinous muscle of neck).—This muscle lies on the arches of the last five cervical vertebræ. It consists of five or six segments.

Origin.—The articular processes of the last five (or four) cervical and the first thoracic vertebræ.

Insertion.—The spinous processes of the cervical vertebræ.

FIG. 179.—DEEPER MUSCLES OF HORSE.

f, Long head of triceps; f′, external head of triceps; g, anterior superficial pectoral; h, posterior deep pectoral; h′, anterior deep pectoral; i, serratus thoracis; i′, serratus cervicis; l, obliquus abdominis externus, and l′, its aponeurosis, the posterior part of which has been removed; m, serratus posticus; p, gluteus medius; r, semitendinosus; s, sacro-coccygeus superior; t, sacro-coccygeus lateralis; u, coccygeus; v′, biceps brachii; x, rhomboideus; y, y′, trachelo-mastoideus; z, supraspinatus; z′, infraspinatus; 1, cartilage of scapula; 2, spine of scapula; 5, external tuberosity of humerus; 6, deltoid tuberosity; 8, olecranon; 16, external angle of ilium; 19, trochanter major; 20, patella; 21′, external condyle of tibia; 26, articular processes of cervical vertebræ; 27, parotido-auricularis; 28, vastus externus; 28′, rectus femoris; 28″, trochanter tertius; 29, semimembranosus; 30, gastrocnemius; 31, sacro-sciatic ligament; 32, omo-hyoideus; 33, complexus; 34, rectus capitis anterior major; 35, spinalis dorsi; 36, longissimus dorsi; 37, transversalis costarum; 38, teres minor; 39, brachialis; 40, external intercostal; 41, obliquus abdominis internus; 42, iliacus; 43, transversus abdominis. (After Ellenberger-Baum, Anat. für Künstler.) ]

Action.—Acting together, to extend the neck; acting singly, to flex and rotate the neck to the opposite side.

Structure.—The muscle is composed of two sets of bundles. The superficial bundles are directed obliquely forward and inward, each passing from an articular process to the spine of the preceding vertebra. The deep bundles are shorter and run straight from an articular process to that of the preceding vertebra.

Relations.—Superficially, the complexus, longissimus, trachelo-mastoideus, and great oblique muscles; deeply, the spinalis muscle, the ligamentum nuchæ, and the arches of the vertebræ.

Blood-supply.—Deep cervical and vertebral arteries.

Nerve-supply.—Dorsal branches of the last six cervical nerves.

8. =Spinalis.=—Described with the longissimus on p. 237.

9. =Obliquus capitis posterior= (s. caudalis) (great oblique muscle of the head).—This is a strong, quadrilateral muscle, which covers the dorso-lateral aspect of the atlas and axis.

Origin.—The side of the spine and the posterior articular process of the axis.

Insertion.—The dorsal surface of the wing of the atlas.

Action.—Chiefly to rotate the atlas, and with it the head, to the same side; also to assist in extending and fixing the atlanto-axial joint.

Structure.—The muscle is composed almost entirely of parallel fleshy fibers directed obliquely forward and outward.

Relations.—Superficially, the skin, the splenius, complexus, trachelo-mastoideus, and mastoido-humeralis muscles; deeply, the arch and spine of the axis, the wing of the atlas, the atlanto-axial joint, the multifidus cervicis, the posterior straight muscles, the occipital and vertebral vessels, and the first and second cervical nerves. The terminal part of the vertebral artery joins the posterior branch of the occipital artery under cover of the muscle.

Blood-supply.—Occipital and vertebral arteries.