_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. [Illustration: 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.