850 



THE NERVOUS SYSTEM. 



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 (nervi clunium superiores). 



Anterior Divisions of the Lumbar Nerves. 



The anterior divisions of the lumbar nerves increase in size from above doAvn- 

 ward. 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 outward behind the Psoas magnus or between its fasciculi, dis- 

 tributing filaments to it and the Quadratus lumborum. The anterior divisions 

 of the four upper nerves give off their branches by a series of anastomotic loops, 

 which are called the lumbar plexus. The anterior division of the fifth lumbar, 

 joined with a branch from the fourth, descends across the base of the sacrum to 

 join the anterior division of the first sacral nerve and assist in the formation of 

 the sacral plexus. The cord resulting from the union of the fifth lumbar and the 

 branch from the fourth is called the lumbo-sacral nerve. 



The Lumbar Plexus. 



The lumbar plexus, so called, is formed by the anastomotic loops above men- 

 tioned. The plexus is narrow above, and often connected with the last dorsal by 



C. withlgthDJI 

 jjio-hypogastric // 



FIG. 503. Plan of the lumbar plexus. 



a slender branch, the (torso-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 varies greatly in different subjects. 

 A plan which is often found is the following : The first lumbar nerve receives a 

 branch from the last dorsal, and gives off two branches, the upper of which sub- 



