578 SPINAL NERVES. 



nerves. It communicates with the ilio-hypogastric branch of the lumbar plexus, 

 and is occasionally connected with the first lumbar nerve by a slender branch, 

 the dorsi-lumbar nerve, which descends in the substance of the Quadratus lum- 

 borum. 



The lateral cutaneous branch of the last dorsal is remarkable for its large size , 

 it perforates the Internal and External oblique muscles, passes downwards over 

 the crest of the ilium, and is distributed to the integument of the front of the hip, 

 some of its filaments extending as low down as the trochanter major. 



LUMBAR NERVES. 



The Lumbar nerves are five in number on each side ; the first appears between 

 the first and second lumbar vertebras, and the last between the last lumbar and the 

 base of the sacrum. 



The roots of the lumbar nerves are the largest, and their filaments the most 

 numerous, of all the spinal nerves, and they are closely aggregated together upon 

 the lower end of the cord. The anterior roots are smaller ; but there is not the 

 same disproportion between them and the posterior roots as in the cervical nerves. 

 The roots of these nerves have a vertical direction, and are of considerable length, 

 more especially the lower ones, as the spinal cord does not extend beyond the first 

 lumbar vertebra. The roots become joined in the intervertebral foramina, and, at 

 their exit, divide into two branches, anterior and posterior. 



The posterior branches of the lumbar nerves diminish in size from above down- 

 wards ; they pass backwards between the transverse processes, and divide into 

 external and internal branches. 



The external branches supply the Erector spinae and Inter-transverse muscles. 

 From the three upper branches cutaneous nerves are derived, which pierce the 

 Sacro-lumbalis and Latissimus dorsi muscles, and descend over the back part of the 

 crest of the ilium, to be distributed to the integument of the gluteal region, some 

 of the filaments passing as far as the trochanter major. 



The internal branches, the smaller, pass inwards close to the articular processes 

 of the vertebrae, and supply the Multifidus spinae and Inter-spinales muscles. 



The anterior branches of the lumbar nerves increase in size from above down- 

 wards. At their origin, they communicate with the lumbar ganglia of the sym- 

 pathetic by long slender filaments, which accompany the lumbar arteries round the 

 sides of the bodies of the vertebrae, beneath the Psoas muscle. The nerves pass 

 obliquely outwards behind the Psoas magnus, or between its fasciculi, distributing 

 filaments to it and the Quadratus lumborum. The anterior branches of the four 

 upper nerves are connected together in this situation by anastomotic loops, and 

 form the lumbar plexus. The anterior branch of the fifth lumbar, joined with a 

 branch from the fourth, descends across the base of the sacrum to join the anterior 

 branch of the first sacral nerve, and assist in the formation of the sacral plexus. 

 The cord resulting from the union of these two nerves is called the lumbo-sacral 

 nerve. 



LUMBAR PLEXUS. 



The Lumbar plexus is formed by the loops of communication between the ante- 

 rior branches of the four upper lumbar nerves. The plexus is narrow above, and 

 occasionally connected with the last dorsal by a slender branch, the dorsi-lumbar 

 nerve ; it is broad below, where it is joined to the sacral plexus by the lumbo-sacral. 

 It is situated in the substance of the Psoas muscle, near its posterior part, in front 

 of the transverse processes of the lumbar vertebrae. 



The mode in which the plexus is formed is the following : The first lumbar 

 nerve gives oft' the ilio-hypogastric and ilio-inguinal nerves, and a communicating 

 branch to the second. The second gives oft" the external cutaneous and genito- 

 crural, and a communicating branch to the third nerve. The third nerve gives a 

 descending filament to the fourth, and divides into two branches, which assist in 



