Promontory

the promontory of the sacrum is the ventral border of the base of sacrum (in the cranial-most part of the sacrum), forming a distinct projection at the base of the sacrum where it articulates with the last lumbar vertebra.

The promontory projects together with the last intervertebral disc into the pelvic inlet and marks the dorsal boundary of the pelvic inlet (also known as the pelvic brim), serving as an important landmark in obstetrics and comparative pelvic morphology.