Anterior sacral foramina

At each end of the transverse ridges, are the four anterior sacral foramina, diminishing in size in line with the smaller vertebral bodies.

The foramina give exit to the anterior divisions of the sacral nerves and entrance to the lateral sacral arteries.

Each part at the sides of the foramina is traversed by four broad, shallow grooves, which lodge the anterior divisions of the sacral nerves.

They are separated by prominent ridges of bone which give origin to the piriformis muscle.