THIGH AND BUTTOCK. 



the iliac crest to the buttock as far as in front of and below the 

 great trochanter. [638] 



Lumbar, Sacral, and Coccygeal. These form the lumbo-sacral 

 plexus, which is arbitrarily divided into the lumbar, sacral 

 (sciatic), and pudendal plexuses. Gray rami communicantes, 

 from the abdominal and pelvic sympathetic cords, cross the 

 vertebrae, under the Psoas, to each nerve. White rami commu- 

 nicantes from the first two (or four) lumbar nerves run to the 

 upper part of the lumbar sympathetic cord; and from the 

 third (or second to fourth) sacral nerves, across the cord, to the 

 pelvic sympathetic plexus. [639] 



LUMBAR PLEXUS. 



This is formed by the first three, and part of the fourth lum- 

 bar nerves, and lies in the Psoas, in front of the transverse 

 processes. The first and second lumbar nerves each divide 

 into upper and lower branches. The upper branch of the 

 first (often getting a branch from the last dorsal) divides 

 into the ilio-hypogastric and ilio-inguinal, which run forward 

 in the abdominal wall. The lower branch of the first joins the 

 upper branch of the second to form the genito-crural. The lower 

 branch of the second, the third, and the part of the fourth 

 each divide into two parts, anterior and posterior; the anterior 

 parts (except sometimes the second) unite to form the obtu- 

 rator; the posterior (larger) parts unite to form the anterior 

 crural. The external cutaneous spring from the backs of the 

 posterior parts of the second and third. Muscular branches to 

 the Quadratus lumborum spring from the upper three or four 

 lumbar (and sometimes last dorsal), and to the Psoas from the 

 second and third (or first to fourth) lumbar nerves near their 

 origins. [641] 



Ilio-hypogastric. The iliac branch (inconstant) descends 

 over the iliac crest, behind the iliac branch of the last thoracic, 

 to the skin on the upper and outer part of the buttock. [642] 



Ilio-inguinal. After passing through the external abdom- 

 inal ring it supplies (cutaneous branches) the abdominal wall 



[279] 



