The lateral sacral arteries, [a. sacrales laterales], which are usually two in number on each side, occasionally but one, arise close together from the posterior division of the internal iliac artery.
One of these arteries is distributed along the upper part, and the other along the lower part of the sacrum in the following manner.
Each artery passes downwards, at the same time inclining somewhat inwards in front of the pyriform muscle and sacral nerves, to reach the inner side of the anterior sacral foramina. Continuing to descend, the lower one approaches towards the middle line, and anastomoses' with the middle sacral artery. Branches from these arteries ramify in front of the sacrum, and supply small offsets to the pyriform muscle and sacral nerves.
Besides these branches, the lateral sacral arteries give off a series of dorsal branches which enter the anterior sacral foramina. Each of these, alter having furnished' (within the foramen) a spinal branch, which ramifies on the bones and membranes in the interior of the sacral canal, escapes by the corresponding posterior sacral foramen, and is distributed upon the dorsal surface of the sacrum.