THE SACRAL PLEXUS 369 



The last two do not divide, but join the coccygeal nerve. 



The posterior division of the coccygeal nerve ends with the 

 above, and supplies the skin over the coccyx. 



The Anterior Divisions. The anterior division of the fifth 

 lumbar receives a branch from the fourth, and, under the 

 name of the lumbosacral cord, joins the first sacral. 



The anterior divisions of the first four sacral nerves escape 

 by the anterior sacral foramina; the fifth, between the sacrum 

 and coccyx; all join with filaments from the sympathetic. 



The first three, with a branch from the fourth, enter into 

 the formation of the sacral plexus. 



The .fourth, its remaining portion, sends branches to the 

 bladder and adjacent viscera, and supplies the levator ani, 

 coccygeus, external sphincter (see Perineal and the Hemor- 

 rhoidal Nerve), and skin of the perineum. It also sends a 

 branch to the fifth sacral. The visceral branches unite with 

 occasional branches from the third sacral and with the sym- 

 pathetic. 



The fifth sacral pierces the coccygeus, supplying it and the 

 skin over the coccyx. Branches from the fourth sacral and 

 the coccygeal nerve join it. 



The anterior division of the coccygeal nerve, very small, 

 pierces the coccygeus and sacrosciatic ligaments, and termi- 

 nates by uniting with the fifth sacral. 



The Sacral Plexus 



The sacral plexus is formed by the anterior divisions of the 

 first, second, third, and part of the fourth sacral nerves, together 

 with the lumbosacral cord. 



The lumbosacral cord, with the first, second, and part of the 

 third sacral nerve, is continued into the upper great branch 

 of the plexus, and the remainder of the plexus forms the lower 

 or smaller branch. 



Branches. Besides these two principal branches, which 

 are, respectively, the great sciatic and the pudic nerves, the 

 upper nerves of the plexus give off the nerves of the pyriformis, 

 quadratus, femoris, obturator internus, and gemelli, as well 

 as the superior and inferior gluteal, small sciatic, and a per- 

 forating cutaneous branch. 

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