LUMBAR PLEXUS. 649 



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 vertebra?, 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 the 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, since the spinal cord 

 does not extend beyond the first lumbar vertebra. The roots become joined 

 in the intervertebral foramina ; and the nerves, so formed, divide at their exit 

 into two branches, anterior and posterior. 



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

 downwards ; they pass backwards between the transverse processes, and divide 

 into external and internal branches. 



The external branches supply the Erector Spina? and Intertransverse mus- 

 cles. From the three upper branches, cutaneous nerves are derived, which 

 pierce the Sacro-lurnbalis 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 pro- 

 cesses of the vertebra?, and supply the Multifidus Spinas and Interspinales 

 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 

 sympathetic by long slender filaments, which accompany the lumbar arteries 

 round the sides of the bodies of the vertebra?, beneath the Psoas muscle. The 

 nerves pass obliquely outwards behind the Psoas Magnus, or between its fasci- 

 culi, 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 

 anterior 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 cord. 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 off the ilio-hypogastric and ilio-inguinal nerves, and a communi- 

 cating branch to the second lumbar nerve. The second gives off 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 forming the anterior crural and obturator nerves ; 



