The anterior branches of the lunzbar 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 vertebrm. 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 anastonzosing 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.
7'he 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 awed ; 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 lunzbar or lunzbo-abdominal pkxus 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 vertebrm 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 series is represented by the nzusculo-cutaneous nerves, and the genito-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 ripper 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 glutmal 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 glutmus 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 inguinal, pubic, or scrotal branch runs parallel to Pou part's ligament, in cotnpany with, but above, the small external cutaneous, reaches the ex ternal ring, and divides into internal terminal branches supplying the skin over the pubis ; and external ones supplying the scrotum in the male, and the labia pudendi in the female.