The Probert Encyclopaedia of Medicine

SACRUM

The sacrum is the portion of the vertebral column between the lumbar vertebrae and the structures of the coccyx. It is composed of five vertebrae which are fused together to form a single bone structure. The sacrum features a median crest which is made of the fused spinous processes of its component vertebrae. Beneath this crest is the sacral canal, a tunnel which runs lengthwise from the top of the sacrum to a hiatus (opening) near the bottom. Four pairs of sacral foramina pierce the sacrum, flanking the medial line, where the intermediate sacral crests are formed by the fused articular processes of the component vertebrae. To the outside of the intermediate sacral crests are the lateral crests, formed by the fused transverse processes of the component vertebrae. In the sacrum, therefore, unlike the upper vertebrae in the spine, the intertransverse ligaments have been replaced by fusion of these processes together. The crests are not represented on the pelvic surface of the sacrum, though the sacral foramina are evident.
Research Sacrum