The Occipital bone consists of three parts arranged around the foramen magnum- a large hole for the passage of the spinal cord. The posterior part is triangular in shape, the apex being upwards, and is convex outwardly in both diameters. About the centre of this surface is a tubercle-the external occipital protuberance-and from this curves out on each side the superior curved lines; a short distance below are the inferior curved lines. On each side of the foramen magnum are the condyles for articulation with the atlas. They are large oval masses of bone with an articulating surface convex in both directions;.

in front and behind are found the anterior and posterior condylar foramina, the former of which transmits the hypoglossal nerve. The basilar process, in front of the foramen magnum, is a stout bar of bone articulating with the body of the sphenoid.

Fig. 41. - The Occipital Bone.

The occipital bone articulates with the two parietals above, with the sphenoid in front and below, externally with the temporals, and below with the atlas.