11. =Rectus capitis posterior major= (s. dorsalis major) (great posterior straight muscle of the head).—This muscle extends from the axis to the occipital bone, in contact with the ligamentum nuchæ. _Origin._—The edge of the spinous process of the axis. _Insertion._—The occipital bone, below and external to the complexus and ligamentum nuchæ. _Action._—To extend the head. [Illustration: FIG. 180.—DEEPEST LAYER OF MUSCLES OF NECK OF HORSE. _a_, Obliquus capitis anterior; _b_, obliquus capitis posterior; _c_, rectus capitis lateralis; _d_, rectus capitis anterior minor; _e_, rectus capitis anterior major; _f_, longus colli; _g_, _g′_, scalenus; _h_, transversalis costarum; _i_, longissimus dorsi; _k_, spinalis et semispinalis; _l_, multifidus dorsi; _m_, multifidus cervicis; _n_, intertransversales; _o_, _o′_, rectus capitis posterior major; _p_, rectus capitis posterior minor; _q_, tendon of insertion of complexus; _1_, lamellar part, _1′_, funicular part of ligamentum nuchæ; _2_, occipital crest; _3_, paramastoid process; _4_, edge of wing of atlas; _5_, transverse, and _6_, articular, processes of cervical vertebræ; _7_, nerves of brachial plexus (cut); _8_, first rib. (Ellenberger-Baum, Anat. d. Haustiere.) ] _Structure._—The muscle is fleshy and may be divided into two parallel portions, superficial and deep. The former blends somewhat with the terminal part of the complexus. The deep portion may be termed the rectus capitis posterior medius. _Relations._—Superficially, the anterior oblique, splenius, and complexus; internally, the ligamentum nuchæ; deeply, the atlas, the occipito-atlantal articulation, and the rectus capitis posterior minor. The dorsal branch of the first cervical nerve appears between this muscle and the small oblique. _Blood-supply._—Occipital artery. _Nerve-supply._—Dorsal branch of the first cervical nerve. 12. =Rectus capitis posterior minor= (s. dorsalis minor) (small posterior straight muscle of the head).—This small muscle lies under cover of the preceding. _Origin._—The dorsal surface of the atlas. _Insertion._—The occipital bone beneath the preceding muscle. _Action._—To assist the preceding muscle. _Structure._—It is fleshy and varies a good deal in volume, being sometimes small and difficult to recognize.[44] On the other hand, it is sometimes double. _Relations._—Superficially, the preceding muscle and the small oblique; deeply, the atlas and the occipito-atlantal articulation. _Blood-supply._—Occipital artery. _Nerve-supply._—Dorsal branch of the first cervical nerve. THE FASCIÆ AND MUSCLES OF THE BACK AND LOINS