Origin by the apex of the triangle from the cranial border of the dorsal arch of the atlas for about two millimeters laterad of the median line. The muscle passes over the ligament which connects the atlas to the occiput and adheres to it.
Insertion into an elongated area on the occipital bone, ventrad of the insertion of the rectus capitis posterior medius for about five millimeters next to the median line.
Relations.—Dorsal surface with the rectus capitis posterior medius. Ventral surface with the posterior atlanto-occipital membrane.
Action.—Assists the rectus capitis posterior major.
M. obliquus inferior ([Fig. 71], b).
Origin from the whole lateral surface of the spine of the axis. The parallel fibres form a thick mass which passes laterad and craniad.
Insertion into the dorsal surface of the transverse process of the atlas along a narrow area near its lateral margin.
Relations.—Outer surface with the rectus capitis posterior major ([Fig. 71], a), the complexus ([Fig. 69], b), and the obliquus superior ([Fig. 71], e). Inner surface with the axis.
Action.—Rotates the head.
M. obliquus capitis superior ([Fig. 71], e; [Fig. 72], e).—This is a triangular muscle passing from the outer border of the atlas laterad of the recti capitis posteriores to the occiput.