504 NERVOUS SYSTEM. 



The Lumbar Plexus (Plexus Lumbalis) is concealed by the 

 psoas magnus muscle, and is placed between it, the lumbar ver- 

 tebrae, and the quadratus lumborum: frequently the roots of the 

 nerves forming this plexus penetrate through the substance of 

 the psoas magnus, and form their unions in it. The plexus is 

 narrow and pointed above, where it commences by the fasci- 

 culus of the last dorsal nerve joining the first lumbar; but it in- 

 creases continually afterwards in breadth, owing to the nerves 

 composing it, successively anastomosing farther and farther from 

 the spinal column. From this plexus proceed three principal 

 trunks: the upper one the Anterior Crural (Criiralis Anterior) is 

 of considerable size; and goes to the skin and the muscles on 

 the front of the lower extremity; the middle, called obturator 

 (Nervus Obturator ius,) is not so large as the preceding, and goes 

 through the obturator foramen to the adductor muscles of the 

 thigh ; the inferior, formed by the whole of the fifth and a fasci- 

 culus from the fourth lumbar nerve, joins the upper part of the 

 sciatic plexus in the pelvis. Besides these, there are several 

 branches of smaller size and of less importance, proceeding from 

 the lumbar plexus. 



The Abdomino-Crural Branches, according to Bichat, are 

 most commonly three in number, and come from the two upper 

 lumbar nerves. The first of them goes obliquely downwards and 

 outwards, in front of the quadratus lumborum, to the posterior 

 part of the spine of the ilium, and runs for a short distance 

 along the crista of the bone: it gives filaments to the iliacus in- 

 ternus, and to the abdominal muscles, where they border on this 

 part of the bone. Some of the filaments become cutaneous, 

 but the main trunk of the nerve reaches the anterior superior 

 spinous process, by going between the transversalis and the in- 

 ternal oblique muscle; it then follows the inguinal arch to the 

 external ring, through which it passes, and is distributed in fila- 

 ments upon the groin, the pubis, and the scrotum. The second 

 or middle branch arises from the plexus near the preceding; it 

 descends along the external margin of the psoas magnus, and 

 crosses the iliacus iriternus, covered by the peritoneum; near 

 the anterior superior spinous process, it gets between the lower 

 margins of the abdominal muscles, and is distributed upon them 

 there: some of its ramifications get also through the external 

 ring, and may be traced to the scrotum. The third, or the 



