SPINAL NERVES. 



701 



* layer of the sheath, at a variable distance 

 from the linea alba, to supply the skin at the 

 anterior part of the abdomen. 



The twelfth dorsal nerve is larger than those 

 that have preceded it, and gives a filament 

 of communication to the anterior branch of 

 the first lumbar nerve. It is directed ob- 

 liquely downwards and outwards, following 

 the course of the last rib, along the lower 

 border of which it runs, passes behind the 

 anterior layer of the transversalis fascia be- 

 tween it and the quadratus lumborum, and, 

 on a level with the apex of the rib, divides 

 into two branches. The cutaneous branch, 

 larger than the abdominal, or continuation of 

 the trunk, perforates, obliquely, the external 

 and internal oblique, gives them some small 

 branches, and then becomes superficial, crosses 

 over the crest of the ilium, and divides into 

 a series of divergent filaments, which lose 

 themselves in the skin of the middle of the 

 glutaeal region. The abdominal branch or con- 

 tinuation of the nerve passes between the in- 

 ternal oblique and transversalis, supplies these 

 muscles, communicates with the first branch 

 of the lumbar plexus, and terminates in the 

 rectus and pyramidaiis, and the skin over 

 them. 



The anterior branches of the lumbar nerves 

 are five in number, intervening between the 

 corresponding branches of the dorsal and 

 sacral nerves. They increase in bulk from 

 above downwards, communicate with each 

 other by anastomosing branches, and with the 

 lumbar ganglia by filaments, which come from 

 the latter, or the main trunks. These fila- 

 ments of communication with the sympathetic, 

 vary in number from two to five, and are in 

 close relation with the convexities of the 

 bodies of the lumbar vertebrae. Several nerves 

 are also given to the supply of the psoas 

 muscle. 



The anterior branch of the first lumbar nerve 

 is small, much resembling the anterior branch 

 of the last dorsal. Having quitted the inter- 

 vertebral foramen, it immediately divides into 

 three branches ; two external and small, viz. : 

 the great and small musculo-cutaneous; the 

 other internal and vertical in direction, and 

 forming the anastomosing branch with the second* 



The anterior branch of the second lumbar 

 nerve, twice as long and broader than the first, 

 gives off the genito- crural and external cuta- 

 neous, and communicates by a long anasto- 

 mosing branch with the third. 



The anterior branch of the third lumbar 

 nerve, nearly twice as large as the second, is 

 directed downwards and outwards, and gives 

 off, at an acute angle, a large external branch, 

 concurring to form the anterior crural, and an 

 internal, the obturator nerve: it communicates 

 with the fourth nerve by one branch con- 

 nected with the main trunk, or by two con- 

 nected with its two branches. 



The anterior branch of the fourth lumbar 

 nerve is somewhat larger than the third. It 

 divides into an external branch connected 

 with the external division of the third, to com- 

 plete the anterior crural; and internal to assist 



in the formation of the obturator. Its ter- 

 minal branch is the anastomosing branch with 

 the fifth, internal to the other two, and ver- 

 tical in direction. 



The anterior branch of the fifth lumbar nerve 

 is the largest of all the series, and terminates 

 in the sacral plexus, and is named the lumbo- 

 sacral nerve. 



The lumbar or lumbo-abdominal plexus is 

 rather intricate, and formed by the anasto- 

 mosis of the anterior branches of the five 

 lumbar nerves. Placed upon the sides of the 

 lumbar vertebras between the transverse pro- 

 cesses, and enveloped by the fasciculi of the 

 psoas muscle, it presents, when the latter are 

 dissected away from it, an irregularly triangu- 

 lar appearance ; the apex of the triangle be- 

 ing above, and the base below. In the former- 

 situation, the nerves forming it are compara- 

 tively delicate, and unite with each nearer 

 the vertebral column than the latter ; it com- 

 municates above with the twelfth dorsal nerve, 

 through the medium of the " dorso-lumbar," 

 and below, with the sacral plexus, through 

 the medium of the " lumbo-sacral " nerve. 

 The branches given off from it may be divided 

 into abdominal and crural: the former being 

 given off from its upper ; the latter, from its 

 inferior or terminal portion. 



The abdominal senes is represented by the 

 musculo-cutaneous nerves, and the genii o-crural. 

 The crural series by the external cutaneous, 

 crural, and obturator. The musculo-cutaneous 

 nerves are two in number: the upper being 

 three or four times larger than the lower. 



The upper musculo-cutaneous (large ab- 

 dominal, ilio-hypogastric, ilio-scrotal) is the 

 highest of the branches of the lumbar plexus, 

 taking its origin from the first lumbar nerve. 

 It makes its appearance from behind the 

 psoas muscle about an inch and a half below 

 the last dorsal nerve, runs obliquely down- 

 wards and outwards across the quadratus 

 lumborum in the subperitoneal tissue, and 

 about an inch above the crest of the ilium, 

 perforates the tendon of the transversalis, and 

 is continued between it and the internal ob- 

 lique to the middle of the crest of the ilium, 

 where it divides into two branches, an ex- 

 ternal and internal. The external passes ob- 

 liquely between the internal and external ob- 

 lique, and at the anterior-third of the crest 

 of the ilium, winding on to the glutaeal re- 

 gion, divides into an anterior and posterior 

 series of filaments ; the one supplying the 

 integument over the tensor vaginae femoris, 

 the other that over the anterior part of the 

 glutaeus medius. The internal branch, or the 

 continuation of the nerve, after a course of an 

 inch or two, communicates with the small 

 musculo-cutaneous by a loop which usually 

 passes round the internal circumflex ilii ves- 

 sels. It then- divides into an abdominal and 

 scrotal branch. The abdominal runs parallel 

 to the corresponding branch of the last dorsal, 

 generally communicates with it, and passes 

 through the tendons of the internal and ex- 

 ternal oblique, and is distributed to the skin 

 at the inner part of the groin. The inguina/, 



