Henry Gray (18251861). Anatomy of the Human Body. 1918.
The middle sacral artery (a. sacralis media) (Fig. 531) is a small vessel, which arises from the back of the aorta, a little above its bifurcation. It descends in the middle line in front of the fourth and fifth lumbar vertebræ, the sacrum and coccyx, and ends in the glomus coccygeum (coccygeal gland). From it, minute branches are said to pass to the posterior surface of the rectum. On the last lumbar vertebra it anastomoses with the lumbar branch of the iliolumbar artery; in front of the sacrum it anastomoses with the lateral sacral arteries, and sends offsets into the anterior sacral foramina. It is crossed by the left common iliac vein, and is accompanied by a pair of venæ comitantes; these unite to form a single vessel, which opens into the left common iliac vein.
The abdominal aorta divides, on the left side of the body of the fourth lumbar vertebra, into the two common iliac arteries (Figs. 531,539). Each is about 5 cm. in length. They diverge from the termination of the aorta, pass downward and lateralward, and divide, opposite the intervertebral fibrocartilage between the last lumbar vertebra and the sacrum, into two branches, the external iliac and hypogastric arteries; the former supplies the lower extremity; the latter, the viscera and parietes of the pelvis.