THE COMMON ILIAC ARTERIES 



613 





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 vertebrae, 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 venae comitantes; these unite to form a single 

 vessel, which opens into the left common iliac vein. 



Middle sacral 



Sup. hemorrhoidal 



Fio. 539. The arteries of the pelvis 



THE COMMON ILIAC 



ARTERIES (AA. njAOffi COMMUNES) (Figs. 531, 539). 



The abdominal aorta divides, on the left side of the body of the fourth lumbar 

 vertebra, into the two common iliac arteries. 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. 



