554 THE ARTERIES 



anastomosing with the other arteries of the aV)dominal wall. As they wind round 

 the l)odies of the vertehrie they pass beneath the chain of the sympathetic nerve, 

 and the upper two beneath the right crus of the diaphragm on the right side, and 

 the left crus on the left side. The right arteries also pass beneath the vena cava 

 inferior, and the two upper on that side beneath the receptaculuni chyli. The 

 arteries on both sides then dip beneath the tendinous arch thrown across the sides 

 of the bodies of the vertebrae by the psoas, and continue beneath this muscle until 

 they arrive at the interval between the transverse processes of the vertebrae and the 

 inner edge of the quadratus lumborum. "Whilst under cover of the psoas they are 

 accompanied l)y two slender filaments of the sympathetic nerve and by the lumbar 

 veins. A little anterior to the transverse processes they are crossed by branches of 

 the luml)ar plexus, and here usually cross in front of the ascending lumliar vein. 

 They now ^Jass behind the quadratus lumborum, with the exception usually of the 

 first, and sometimes of the last, which may pass in front of the muscle. At the 

 outer edge of the quadratus they run between the transversalis and the internal 

 obli(jue, and then, perforating the internal oblique, between the internal and 

 external oblique. Finally, much diminished in size, they enter the rectus, and give 

 off one or more anterior cutaneous branches, which accompany the last dorsal and 

 the ilio-hypogastric nerves to the skin. They anastomose with the lower intercos- 

 tals, ilio-lumbar, deep circumflex iliac, and deep epigastric arteries. 



The lumbar arteries give off the following branches: — 



(^(1) Vertebral branches which supply the bodies of the vertebrae and their 

 connecting ligaments. 



(l)) Muscular branches to the psoas, quadratus lumborum, and oblique 

 muscles of the abdomen. 



(c) The dorsal branch. This is of large size, and passes baclcAvards in com- 

 pany with the dorsal nerve between the transverse processes above and below, the 

 intertransversalis internally, and the quadratus lumborum externally, to the 

 muscles of the Ijack. On reaching the interval Ijetween the longissimus dorsi and 

 multifidus spinte, it divides into an external and internal branch. The former 

 ends in the multifidus, the latter and larger supplies the erector spina^, and gives 

 l)ranches which accompany the termination of the dorsal nerves to the skin. Just 

 Ijefore the artery passes betw^een the transverse processes it gives off a spinal branch, 

 which accompanies the lumbar nerve through the intervertebral foramen into the 

 spinal canal. Here the spinal branch divides into three twigs, one of which passes 

 through the sheath of the dura mater to the termination of the spinal cord and 

 Cauda equina; the other two are distrilmted to the walls of the spinal canal after 

 the way descril^ed in the case of the intercostals. 



((/) Renal branches of small size pass forwards in front of the quadratus lum- 

 borum to the ca})sule of the kidney. The}^ anastomose with the renal artery. A 

 conmnmication is thus established between the renal arteries and the arteries 

 su])plying the lumljar region. 



The fifth pair of lumbar arteries, when present, usually come off from the 

 middle sacral artery. Each courses outwards, l^eneath the common iliac artery 

 and vein; and, after giving off a dorsal branch, ramifies over the lateral mass of the 

 sacrum, and ends in the iliacus muscle l)y anastomosing with the circumflex iliac 

 artery. The dorsal branch passes to the back l)etween the last lumbar vertebra 

 and the sacrum and ramifies in the gluteus maximus, anastomosing with the 

 luml)ar arteries above, and with the gluteal artery below. 



The variations in the lumbar arteries are not of erreat importance. (A) One or more pairs 

 may arise as a common stem from the back of tlie aorta. (B) The first lumbar may be joined at 

 its oriiiin with the sul)oostal artery ; or the third and fourtli luud)ar, or less often the second and 

 third lumbar, may arise from the aorta as a common stem. (C) The fii'th pair may sometimes 

 be absent. _(D) The first lumbar may give off the phrenic or the suprarenal. (E) One of the 

 lumbar arteries may give off the spermatic. (F) The fourth lumbar on either side may give off' 

 the middle sacral, or both arteries may arise as a common stem with the middle sacral. 



