312 



THE SPINAL NERVES. 



LUMBAR PLEXUS. 



The lumbar plexus is formed by the anterior primary divisions of the upper four 

 lumbar nerves. It is placed in the substance of the psoas muscle, in front of the 

 transverse processes of the corresponding vertebrae. Above, the plexus is narrow, 

 and is usually connected with the last dorsal nerve by a small offset from that nerve, 



DXTT 



IV 



V 



CJ 



Fig. 204. DIAGRAM OF THE LUMBAR AND 

 SACRAL PLEXUSES WITH THE PRINCIPAL 

 NERVES ARISING FROM THKM. (Allei) 



Thomson.) % 



DXII, the divided roots of the last dorsal 

 nerve ; LI, to V, the roots of the five 

 lumbar nerves ; the loops uniting the an- 

 terior primary divisions of these nerves 

 together, and the first with the twelfth 

 dorsal, are shown ; SI, to V, and CI, the 

 sacral and coccygeal nerves ; p, placed on 

 some of the nerves, marks the posterior 

 primary divisions cut short ; p, p', the 

 plexus formed by the union of the posterior 

 branches of the third, fourth, and fifth sacral 

 and the coccygeal nerves ; d, anterior divi- 

 sion of the last dorsal nerve, from which 

 d' the lateral cutaneous branch arises ; 1,1', 

 ilio-hypogastric nerve, dividing into its two 

 branches ; the ilio-inguinal nerve is seen 

 below these, without a number ; 2, genito- 

 crural ; 2', external cutaneous of the thigh ; 

 ql, branches to quadratus lumborum ; %.s, 

 branches to the psoas muscle ; a; anterior 

 crural nerve ; il, branches to the iliacus ; 

 ob, obturator nerve ; ob', accessory obturator ; 

 IV, V, loop from the fourth and fifth 

 lumbar, forming the lumbo-sacral cord ; 



3, superior gluteal nerve ; sc, great sciatic 

 nerve, continued from the sacral plexus ; 



4, small sciatic nerve rising from the plexus 

 posteriorly ; 4', inferior gluteal nerve ; 5, 

 inferior pudendal ; 5', posterior cutaneous of 

 the thigh and leg ; 6, 6, branch to the 

 obturator internus and gemellus superior ; 

 b", (>', branch to the gemellus inferior, 

 quadratus femoris and hip-joint ; 7, twigs to 

 the pyriformis ; 8, pudic nerve ; 9, visceral 

 branches ; 9', twig to the levator ani ; 10, 

 perforating cutaneous nerve; 11, coccygeal 

 branches. 



named dor so-lumbar ; below, it is 

 wider, and is joined to the sacral 

 plexus by means of a branch passing 

 from the fourth lumbar nerve to the 

 fifth. 



The nerves entering the lumbar 

 plexus do not form an interlace- 

 ment, as in the brachial plexus, but the several nerves of distribution proceeding 

 from the plexus for the most part arise by two or more roots from a corre- 

 sponding number of spinal nerves, so as to produce the appearance of a series 

 of loops. The usual arrangement may be thus stated : The first lumbar nerve, 

 having been joined by the branch from the last dorsal, gives off the ilio- 

 hypogastric and ilio-inguinal nerves, and sends downwards a communicating 

 branch to the second nerve. The fibres of the dorso-lurnbar cord enter chiefly 

 the ilio-hypogastric nerve, but some may pass also to the ilio-inguinal. The 



