77^ A MANUAL OF ANATOMY 



more particularly the upper or outer band of that plexus which is 

 continued into the great sciatic nerve. 



The anterior primary division of the fourth lumbar nerve is known 

 as a nervus furcalis from the fact that it is distributed partly to the 

 lumbar and partly to the sacral plexus. 



Lumbar Arteries. — These are branches of the abdominal aorta, 

 being parietal in their distribution, and they are serially continuous 

 with the aortic intercostal and subcostal arteries. They are eight 

 in number, four right and four left, and they arise in pairs, separately 

 or conjointly, from the posterior aspect of the parent trunk. They 

 occupy the grooves at the centres of the bodies of the first four 

 lumbar vertebrae. As each artery winds round a vertebral body 

 it passes beneath one of the fibrous arches of the psoas magnus and 

 the lumbar sympathetic gangliated cord. It then passes behind 

 the psoas magnus and lumbar plexus, and, on reaching the interval 

 between two adjacent lumbar transverse processes, it divides into 

 two branches, dorsal and abdominal. The upper two arteries pass 

 beneath the corresponding crus of the diaphragm, and those of the 

 right side also pass beneath the receptaculum chyli and right azygos 

 vein. All four arteries on the right side pass beneath the inferior 

 vena cava. The trunk of each lumbar artery gives off a few 

 vertebral branches to the body and ligaments of the adjacent 

 vertebra, and muscular branches to the psoas magnus. The dorsal 

 branch passes backwards between the adjacent transverse processes, 

 in company with the posterior primary division of a spinal nerve, 

 and it divides into an internal and external branch. The internal 

 branch supplies the multifidus spinse, and the external branch 

 supplies the erector spinse, giving also cutaneous branches which 

 accompany the cutaneous nerves to the integument. Opposite an 

 intervertebral foramen the dorsal branch furnishes a spinal branch, 

 which enters the spinal canal through the foramen, to be distributed 

 to the spinal cord and its coverings, as well as to the wall of the 

 canal. 



The abdominal branch is to be regarded as the continuation of a 

 lumbar artery. These branches usually pass behind the quadratus 

 lumborum, with the exception, as a rule, of that of the fourth. At 

 the outer border of that muscle they pierce the posterior aponeurosis 

 of the transversal is abdominis, and pass forwards between that 

 muscle and the internal oblique, as far as the lower part of the 

 rectus abdominis, which they enter. They furnish the following 

 offsets, in order : muscular to the quadratus lumborum ; capsular 

 to the capsule of the kidney, which anastomose with branches of 

 the renal artery ; subperitoneal to the subperitoneal areolar tissue, 

 which anastomose therein with branches of the ilio-lumbar, the 

 mferior phrenic, and the hepatic, colic, and renal arteries, thus 

 forming the subperitoneal arterial plexus of Turner ; muscular to 

 the abdominal muscles, which anastomose above with the lower 

 two intercostal and subcostal arteries, below witli the lateral or 

 intermuscular epigastric of the deep circumflex iliac, and ilio-lumbar, 



