428 ARTERIES. 



the body of the corresponding lumbar vertebra, behind the sympathetic nerve 

 and the Psoas muscle ; those on the right side being covered by the inferior vena 

 cava, and the two upper ones on each side by the crura of the Diaphragm. In the 

 interval between the transverse processes of the vertebras, each artery divides 

 into a dorsal and an abdominal branch. 



The dorsal branch gives off) immediately after its origin, a spinal branch, 

 which enters the spinal canal; it then continues its course backwards, between 

 the transverse processes, and is distributed to the muscles and integument of the 

 back, anastomosing with its fellow, and with the posterior branches of the inter- 

 costal arteries. 



The spinal branch, besides supplying offsets which run along the nerves to the 

 dura mater and cauda equina, anastomosing with the other spinal arteries, divides 

 into two branches, one of which ascends on the posterior surface of the body of 

 the vertebra above, and the other descends on the posterior surface of the body of 

 the vertebra below, both vessels anastomosing with similar branches from neigh- 

 boring spinal arteries. The inosculations of these vessels on each side, throughout 

 the whole length of the spine, form a series of arterial arches behind the bodies 

 of the vertebras, which are connected with each other, and with a median longi- 

 tudinal vessel, extending along the middle of the posterior surface of the bodies 

 of the vertebras, by transverse branches. From these vessels offsets are distributed 

 to the periosteum and bones. 



The abdominal branches pass outwards, behind the Quadratus lumborum, the 

 lowest branch occasionally in front of that muscle, and, being continued between 

 the abdominal muscles, anastomose with branches of the epigastric and internal 

 mammary in front, the intercostals above, and those of the ilio-lumbar and circum- 

 flex iliac, below. 



MIDDLE SACRAL ARTERY. 



The Middle Sacral Artery is a small vessel, about the size of a crow-quill, 

 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 terminates by anastomosing 

 with the lateral sacral arteries. From it, branches arise which run through the 

 rnesorectum, 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 

 off small offsets which enter the anterior sacral foramina. 



COMMON ILIAC ARTERIES. 



The abdominal aorta divides into the two common iliac arteries. The bifurcation 

 usually takes place on the left side of the body of the fourth lumbar vertebra. 

 This point corresponds to the left side of the umbilicus, and is on a level with a 

 line drawn from the highest point of one iliac crest to the other. The common 

 iliac arteries are about two inches in length; diverging from the termination of the 

 aorta, they pass downwards and outwards to the margin of the pelvis, and divide 

 opposite the intervertebral substance, between the last lumbar vertebra and the 

 sacrum, into two branches, the external and internal iliac arteries; the former 

 supplying the lower extremity ; the latter, the viscera and parietes of the pelvis. 



The right common iliac is somewhat larger than the left, and passes more ob- 

 liquely across the body of the last lumbar vertebra. It is covered by the peri- 

 toneum, the ileum, the branches of the sympathetic nerve ; and crossed, at its 

 point of division, by the ureter. Behind, it is separated from the last lumbar 

 vertebra, by the two common iliac veins. On its outer side, it is in relation with 

 the inferior vena cava, and right common iliac vein, above ; and the Psoas magnus 

 muscle, below. 



The left common iliac is in relation, in front, with the peritoneum, branches of 

 the sympathetic nerve, the rectum and superior hemorrhoidal artery ; and crossed, 

 ;:t its point of bifurcation, by the ureter. The left common iliac vein lies partly 



