498 DISSECTION OF THE ABDOMEN. 



of the spinal column (fig. 1 72) ; it lies along the inner border of the psoas 

 muscle, nearer the front of the vertebra than in the thorax, and is some- 

 what concealed on the right side by the vena cava. The cord possesses 

 four or five oblong ganglia opposite the bodies of the vertebrae, which sup- 

 ply connecting and visceral branches. 



Connecting branches. From each ganglion two small branches are di- 

 rected backwards along the centre of the body of the vertebra, with the 

 lumbar artery ; these unite with one or two spinal nerves near the inter- 

 vertebral foramen. The connecting branches are long in the lumbar 

 region in consequence of the gangliated cord being raised by the psoas 

 muscle to the fore part of the vertebrae. 



Branches of distribution. Most of the internal branches throw them- 

 selves into the aortic and hypogastric plexuses, and so reach the viscera 

 indirectly. Some filaments enter the vertebrae and their connecting liga- 

 ments. 



Last dorsal nerve (fig. 172, e). The anterior primary branch of the 

 last dorsal resembles the intercostal nerves in its distribution, but differs 

 from them in not being contained in an intercostal space. Lying below 

 the last rib, the nerve is directed outwards across the upper part of the 

 quadratus lumborum, and beneath the fascia covering that muscle, as far 

 as the aponeurosis of the transversalis abdominis (fascia lumborum); here 

 it enters the wall of the abdomen, and ends in an abdominal and a cuta- 

 neous branch (p. 4 1C). The lowest intercostal artery accompanies it. 



Near the spine it furnishes a small branch to the quadratus muscle ; and 

 it may communicate by means of this with the first lumbar nerve. 



The LUMBAR ARTERIES of the aorta (p. 489), are furnished to the Back, 

 the spinal canal, and the wall of the abdomen : they resemble the aortic 

 intercostals in their course and distribution. Commonly four in number 

 on each side, they arise opposite the centre of the lumbar vertebrae, and 

 the vessels of opposite sides are sometimes joined in a common trunk ; 

 they then pass backwards beneath the pillar of the diaphragm and the 

 psoas, to reach the interval between the transverse processes, where each 

 ends in an abdominal and a dorsal branch. The arteries of the right side 

 lie beneath the vena cava. 



The dorsal branch continues to the Back between the transverse pro- 

 cesses, and supplies an offset to the spinal canal (pp. 368, 384). 



The abdominal branches are directed outwards beneath the quadratus 

 lumborum, and enter the posterior part of the abdominal wall, where they 

 anastomose with the lower intercostal above, and with the circumflex iliac 

 and ilio-lumbar arteries below : these branches supply the psoas and quad- 

 ratus muscles; and the last furnishes an offset to the teguments with the 

 ilio-hypogastric nerve. 



The LUMBAR VEINS are the same in number, and have the same course 

 as the arteries. Commencing by the union of a dorsal and an abdominal 

 branch at the root of the transverse process, each trunk is directed for- 

 wards to the vena cava. They open into the posterior part of the cava, 

 either singly, or conjointly with those of the opposite side. On the left 

 side the veins are longer than on the right, and pass beneath the aorta. 



Around the transverse processes, and beneath the psoas muscle, the lum- 

 bar veins communicate freely wjth one another, with the ilio-lumbar, and 

 sometimes with the common iliac, so as to form a plexus of veins. Issuing 

 from the upper part of the plexus is a small branch, the ascending lumbar 

 vein, which joins the azygos vein of the corresponding side of the body. 



