LUMBAR NERVES. 857 



slender, which passes over the external intercostal muscle to be expended in its 

 substance, before arriving: at the sternum. Tlie second pair also concurs in the 

 formation of the brachial plexus, tliouijli only by a small branch. 



Article III. — Lumbar Nerves (G Pairs). 



Superior Branches. — Distributed to the spinal muscles and the integu- 

 ments of the loins and croup, these are larg;er than the corresponding branches 

 of the dorsal region, but present an analogous disposition. They give superior 

 ramuscules to the muscles of the spine, and very long external divisions which 

 pass through these muscles, to be distributed to the skin of the croup. 



Inferior Branches.— The AVs/— comprised in the interval separating the 

 last rib from the first lumbar transveree process, between the quadratus lumborum 

 and the psoas magnus — passes downwards and backwards until it arrives between 

 the transverse and internal obli(]ue muscles of the abdomen, to which it gives 

 filaments, and is finally distributed in the rectus abdominis muscle. 



Above the superior border of the internal oblique nmscle, it funiishes a per- 

 forating branch to the skin of the flank and the posterior part of the panniculus 

 carnosus. 



The second, disposed in the same manner as the preceding, follows an analogous 

 course, and breaks up into several divisions which are lost in the internal oblique 

 muscle. From one of these sometimes emanates a slender filament, which joins 

 one of the inguinal nerves of the third pair. We must not overlook, in the 

 enumeration of the branches emitted by this second pair of lumbar nerves, the 

 two perforating branches which descend in front, and on the inside, of the thigh, 

 to be distributed to the skin of the flank and the internal crural region. 



The t/tird^ also passes outwards, above the psoas muscles, which receive 

 from it several divisions, and ramifies in the muscles of the flank. It has also 

 perforating nerves, destined to the inguinal region, and these comport them- 

 selves in a sufficiently interesting manner to merit particular mention. They 

 are usually three in number — an infern/d and two exterunl inguinal nerves. 

 The three pass at first beneath the peritoneum, and are directed backwards, 

 downwards, and outwards, towards the inguinal canal, which they enter — one 

 to the inside, the other to the outside of the spermatic cord. They give off 

 some filaments to the cremaster and abdominal muscles, and at last ramify 

 in the envelopes of the testicle, the sheath, and the skin of the inguinal region. 

 The two external nerves are often confounded in a single trunk, on their arrival 

 at the cremasteric muscle. The disposition they affect at their origin is 

 extremely variable ; sometimes they have each a distinct commencement, and 

 separately tra\erse either the small or large psoas muscle, or the space between 

 these ; and, at other times, the internal and one of the external inguinal nerves 

 proceed from a common trunk at the intervertebral foramen, the second external 

 nerve then arising alone towards the external border of the psoas magnus 

 muscle. Most frequently, the internal nerve receives a branch from the fourth 

 pair, and it is even sometimes entirely formed by that branch. This variation 

 in arrangement is not, however, the exclusive appanage of the inguinal nerves ; 

 we have seen the third pair alone furnish these three nerves and the filaments 

 to the psoas muscles, without being prolonged into the muscles of the flank. 



The fourth ^ pierces the psoas parvus muscle, and enters the space separating 



' Representing the abdomino-genital and femnro-genital branches of Man. 

 ' The femoro-cutaneous branch of the lumbar plexus of Man. 



