The lateral part of sacrum is broad above, but narrowed into a thin edge below.
The upper half presents in front an ear-shaped surface, the auricular surface,covered with cartilage in the fresh state, for articulation with the ilium.
Behind it is a rough surface, the sacral tuberosity, on which are three deep and uneven impressions, for the attachment of the posterior sacroiliac ligament.
The lower half is thin, and ends in a projection called the inferior lateral angle; medial to this angle is a notch, which is converted into a foramen by the transverse process of the first piece of the coccyx, and transmits the anterior division of the fifth sacral nerve.
The thin lower half of the lateral surface gives attachment to the sacrotuberous and sacrospinous ligaments, to some fibers of the Glutæus maximus behind, and to the Coccygeus in front.