sacral foramina (anterior and posterior)
sa·cral fo·ra·mi·na (anterior and posterior)[TA]
the openings between the fused sacral vertebrae transmitting the sacral nerves. The anterior sacral foramina transmit anterior (ventral) primary rami of the sacral nerves. The posterior sacral foramina give passage to posterior (dorsal) primary rami of the sacral nerves. The terms "anterior" and "posterior" are awkward with regard to the S1/S2 foramina especially because in the anatomic position the foramina lie vertically, superior and inferior, to each other.