THE FOURTH AND FEFTH SACRAL NERVES. 323 



only a short space, these three nerves may be noticed first, before the other nerves 

 and the numerous branches to which they give rise are described. 



FOURTH SACRAL NERVE. 



Only one part of the anterior division of this nerve joins the sacral plexus ; the 

 remainder, which is more than half the nerve, supplies branches to the viscera and 

 muscles of the pelvis, and sends downwards a connecting filament to the fifth 

 nerve. 



(a) The visceral branches of the fourth sacral nerve are directed forwards to the 

 lower part of the bladder, and communicate freely with branches from the sympa- 

 thetic nerve. Offsets are distributed to the neighbouring viscera, according to the 

 sex (nn. hfemorrhoidales medii ; nn. resicales inferiores ; nn. vtujinales). They will 

 be described with the pelvic portion of the sympathetic nerve. These branches are 

 associated with others proceeding from the third sacral nerve, and they are some- 

 times derived mainly from the latter nerve. Sometimes filaments are added from 

 the second sacral nerve. 



(Jb) Of the muscular branches, one supplies the levator ani, piercing that muscle 

 on its pelvic surface ; another enters the coccygeus ; while a third (hcemorrhoidal or 

 penneal branch} ends in the external sphincter muscle of the anus. The last branch, 

 after passing either through the coccygeus, or between it and the levator ani, reaches 

 the perineum, and gives filaments also to the integument between the anus and the 

 coccyx. 



According 1 to Eisler the nerve to the levator ani is derived from the third and fourth sacral 

 nerves, in some cases even from the second and third. 



FIFTH SACRAL NERVE. 



The anterior branch of this, the lowest sacral nerve, comes forwards through the 

 coccygeus muscle opposite the junction of the sacrum with the first coccygeal 

 vertebra : it then descends upon the coccygeus nearly to^the tip of the coccyx, where 

 it turns backwards through the fibres of that muscle, and ends in the integument 

 upon the posterior and lateral aspect of the bone (nn. ano-coccygei). 



As soon as this nerve appears in front of the coccygeus muscle (in the pelvis) it 

 is joined by the descending filament from the fourth nerve, and lower down by the 

 small anterior division of the coccygeal nerve. It supplies filaments to the coccygeus 

 muscle. 



COCCYGrEAL NERVE. 



The anterior branch of the coccygeal, or, as it is sometimes named, the sixth 

 sacral nerve, is a very small filament. It escapes from the spinal canal by the 

 terminal opening, pierces the sacro-sciatic ligaments and the coccygeus muscle, and, 

 being joined upon the side of the coccyx with the filth sacral nerve, partakes in the 

 distribution of that nerve. The connection between the fourth and fifth sacral and 

 the coccygeal nerves is sometimes described as the coccygeal plexus. 



SACRAL PLEXUS. 



The lumbo-sacral cord (resulting as, before described from the junction of the 

 fifth and part of the fourth lumbar nerves), the anterior divisions of the first three 

 sacral nerves, and part of the fourth unite to form this plexus. Its construction is 

 simpler than that of the spinal nerve-plexuses already described, as the several 

 nerves unite without much interlacement into an upper large, and a lower small, cord 

 or band. The upper band is formed by the union of the lumbo-sacral cord with the 

 first and second, and the greater part of the third, sacral nerves, and is continued 



