_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. _Nerve-supply._—Dorsal branch of the second cervical nerve. 10. =Obliquus capitis anterior= (s. cranialis) (small oblique muscle of the head).—A short, thick, quadrilateral muscle which lies on the side of the occipito-atlantal articulation. _Origin._—The anterior edge of the wing of the atlas and the fossa atlantis. _Insertion._—The styloid process and crest of the occipital bone, and the mastoid process. _Action._—Acting together, to extend the head on the atlas; acting singly, to flex the head laterally. _Structure._—The muscle contains a good deal of tendinous tissue. The direction of its fibers is forward, upward, and inward. _Relations._—Superficially, the posterior auricular muscles, artery, and nerve, the aponeurosis of the splenius, trachelo-mastoideus and mastoido-humeralis, and the parotid gland; deeply, the straight muscles, the complexus, the occipito-hyoideus, the occipito-atlantal articulation, branches of the occipital artery, and a branch of the occipital nerve. _Blood-supply._—Occipital artery. _Nerve-supply._—Dorsal branch of the first cervical nerve.