THE COMPOSITE NERVES. 753 



supersacral foramen, reach the muscles lodged on the sides of the sacral 

 spine, and terminate in the skin of the croup. 



INFERIOR BRANCHES. Thick nervous trunks, 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 ischiatic 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 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 after- 

 wards descends on the dorsal border of the penis in the midst of the magni- 

 ficent 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, whose ultimate ramifications enter the corpora 

 cavernosa, or go to the urethral canal ; before leaving the pelvis, it gives off, be- 

 hind, two thin ramuscules destined to the muscles and skin of the perineo-anal 

 region. These ramuscules, like the principal trunk, receive anastomotic fila- 

 ments from one of the ischio-muscular branches of the lumbo-sacral plexus. 



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

 the preceding, and is distributed to the sphincter muscle and the surround- 

 ing integuments. Before quitting the pelvis, it gives a ramuscule to the 

 levator ani. 



The five inferior sacral branches emit, near their origin, a more or less 

 slender filament that proceeds to the pelvic or hypogastric plexus. The 

 anastomotic divisions, through which they communicate with the sympathetic 

 chain, are generally thick, short, and multiple. 



ARTICLE V. COOCYGKAL NERVES (6 to 7 Pairs). 



In the coccygeal region are found two pairs of nerves, one placed 

 beneath the depressor muscle of the tail, the other below the lateral 

 sacro- coccygeal muscle. These two nerves extend to the extremity of the 

 tail, throwing off on their track some muscular and cutaneous filaments. 

 They are formed by the superior and inferior branches of the coccygeal 

 nerves, which gradually amalgamate to form the two trunks. 



These coccygeal branches are six or seven in number, and very distinct ; 

 they diminish in volume from the first to the last. The first only gives a 

 slender filament for the formation of each coccygeal trunk ; it is chiefly 

 expended in the integuments and muscles at the base of the tail. 



ARTICLE VI. COMPOSITE NERVES FORMED BY THE INFERIOR BRANCHES OP 



THE SPINAL NERVES. 



We already know that these nerves represent three groups : 1, The 

 diaphragmatic nerve ; 2, The brachial plexus ; 3, The lumbo-sacral plexus. 

 They will be studied in this order. 



