670 



THE VASCULAR SYSTEMS 



of the back. It gives off a spinal branch (ramus spinalis) which enters the vertebral 

 canal and is distributed in a similar manner to the lateral spinal branches of the 

 vertebral (page 622). Muscular branches are supplied from each lumbar artery 

 and from its dorsal branch to the neighboring muscles. 



The middle sacral artery (a. sacralis media) (Fig. 473) is a small vessel, 

 which arises from the back part of the aorta just at its bifurcation. It descends 

 upon the last lumbar vertebra, and along the middle line of the front of the sacrum, 

 to the upper part of the coccyx, where it anastomoses with the lateral sacral 

 arteries, and terminates in the coccygeal body. From it minute branches arise 

 which run through the mesorectum to supply the posterior surface of the rectum. 

 Other branches are given off on each side, which anastomose with the lateral sacral 

 arteries, and send branches into the anterior sacral foramina. It is crossed by the 

 left common iliac vein, and is accompanied by a pair of venae comites; these 

 unite to form a single vessel which opens into the left common iliac vein. 



This artery and its lateral branches probably represent fused segmental arteries 

 (see page 766). 



THE COMMON ILIAC ARTERIES (AA. ILIACAE COMMUNES) (Figs. 467, 473). 



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 two inches in length. 

 They diverge from the termination of the aorta, pass downward and outward to 

 the margin of the pelvis, and divide, opposite the intervertebral disk, between the. 

 last lumbar vertebra and the sacrum, into two branches, the internal and external 

 iliac arteries, the latter supplying the lower extremity; the former, the viscera and 

 parietes of the pelvis. 



The right common iliac is somewhat longer than the left, and passes more 

 obliquely across the body of the last lumbar vertebra. In front of it are the peri- 

 toneum, the small intestines, branches of the sympathetic cord, and, at its point 

 of division, the ureter. Behind, it is separated from the bodies of the fourth and 

 fifth lumbar vertebra?, and the intervening intervertebral disk, by the two common 

 iliac veins. On its outer side, it is in relation above with the inferior vena cava 

 and the right common iliac vein; and below, with the Psoas magnus muscle. On 

 its inner side, above, is the left common iliac vein. 



The left common iliac is in relation, in front, with the peritoneum, small intes- 

 tines, branches of the sympathetic cord, and the superior hemorrhoidal artery; 

 and is crossed at its point of bifurcation by the ureter. It rests on the bodies of the 

 fourth and fifth lumbar vertebrae, with the intervening disk. The left common 

 iliac vein lies partly on the inner side, and partly behind the corresponding artery; 

 on its outer side, the artery is in relation with the Psoas magnus muscle. 



PLAN OF THE RELATIONS OF THE COMMON ILIAC ARTERIES. 



In front. 

 Peritoneum. 

 Small intestines. 

 Sympathetic cord. 

 Ureter. 



Outer side. 



Inferior vena cava. 

 Right common 



iliac vein. 

 Psoas muscle. 



Behind. 



Fourth and fifth lumbar vertebrae. 

 Right and left common iliac veins. 



Inner side. 



Left common 

 iliac vein. 



In front. 

 Peritoneum. 

 Sympathetic cord. 

 Superior hemorrhoidal artery. 

 Ureter. 



Outer side. 



Psoas magnus 

 muscle. 



Behind. 



Fourth and fifth lumbar vertebrae. 

 Left common iliac vein. 



