858 THE NERVES. 



it from its congener — the psoas magnus. 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 

 tensor 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 gives : 1. A thick, short branch to the psoas magnus muscle. 

 2. A large anastomosing branch which concurs in the formation of the lumbo- 

 sacral plexus. 3. A filament that joins the internal inguinal nerve furnished bj 

 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 plexus of the abdominal limb. 



All the inferior lumbar branches communicate with the sympathetic by 

 several filaments, which pass across the fasciculi of the psoas parvus 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. 



Aeticle IV. — Sacral Nerves (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. 



Superior Branches. — These are small ramuscules that pass through the 

 supra-sacral foramen, reach the muscles lodged on the sides of the sacral spine, 

 and terminate in the skin of the croup. 



Inferior Branches. — Thick nerves, which diminish in volume from the 

 first to the fifth, and leave the sacral canal to pass downwards and backwards on 

 the sides of the pelvic cavity. 



The first, second, and third are directed towards the great sciatic opening, 

 and are united into a wide nervous band that constitutes the pelvic portion of 

 the lumbo-sacral plexus, to be described at another time. 



The fourth and fifth course along the side of the pelvic cavity — in the 

 texture of the sacro-sciatic ligament, or even within it ; united at their base by 

 an anastomosing filament, they do not usually communicate — at least, in a direct 

 manner — with the fasciculus formed by the three first pairs. 



The fourth constitutes the internal pudic nerve, which passes between the 

 two roots of the corpora cavernosa in bending round the ischial arch, where 

 it lies nearly alongside its fellow of the opposite side. This nerve afterwards 

 descends on the dorsal border of the penis, in the midst of the magnificent 

 venous plexus of that organ, describing flexuosities which allow it to adapt 

 itself to the elongation of the penis. Arriving at the extremity of the organ, 

 it terminates in numerous divisions in the proper erectile tissue of this part, 

 or in the mucous membrane covering it. On its course it emits very long 

 flexuous branches, the ultimate ramifications of which enter the corpora caver- 

 nosa, or go to the urethral canal. Before leaving the pelvis, it gives off", behind, 

 two thin ramuscules to the muscles and skin of the perineo-anal region. These 

 ramuscules, like the principal trunk, receive anastomotic filaments from one of 

 the ischio-muscular branches of the lumbo-sacral plexus. 



The fifth is the anal or hcemorrhoidal nerve. It passes backward, above 



