752 THE NERVES. 



The third,^ also passes outwards, above the psoas muscles, which receivs 

 from it several divi sions, and ramifies in the muscles of the flank. It has 

 also perforating nerves, destined to the inguinal region, and these comport 

 themselves in a sufficiently interesting manner to merit particular mention. 

 They are usually three in number : an internal and two external 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 cremaster muscle. The 

 disposition they affect at their origin is extremely variable ; sometimes they 

 have each a distinct commencement, and separately traverse 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 tha external border of the great psoas 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 only supply these three nerves and the filaments of the 

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



The/oMriA^ pierces the small psoas muscle, and enters the space separating 

 it from its congener — the great psoas. After passing between the peritoneum 

 and the lumbo-iliac aponeurosis, it arrives below the angle of the haunch, 

 and makes its exit from the abdomen ; it then descends within, and in front 

 of, the fascia lata muscle, and accompanying the divisions of the circumflex 

 iliac artery, it is prolonged to the stifle, where it is expended in the skin. 

 At its origin, it abandons : 1, A thick, short branch to the great psoas 

 muscle ; 2, A large anastomosing branch which concurs in the formation of 

 the lumbo-saoral plexus ; 3, A filament that joins the internal inguinal 

 nerve furnished by the third pair. We have already mentioned that this 

 nerve sometimes emanates entirely from the fourth pair. 



The fifth and sixth, much more voluminous than the preceding, unite, 

 and, with the three first sacral pairs, form the nervous plexus of the 

 abdominal limb. 



All the inferior lumbar branches communicate with the great sympathetic 

 by several filaments, which pass across the fasciculi of the small psoas muscle ; 

 and all communicate with each other : the two last by fusion of their fibres, 

 and the first five by means of more or less voluminous anastomotic branches 

 which are far from being constant. 



Article IV.— Saokal Nebves (5 Pairs). 



We describe, as sacral nerves, not only the four double cords which 

 escape by the lateral foramina of the os sacrum, but also the nerve that 

 passes through the intervertebral foramen between that bone and the last 

 lumbar vertebra. 



SuPEEioB Bkanohes. — Thesc are small ramusoules that pass through the 



' Representing the abdomino-genifal and femoro-genital branches of Man. 

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



