DISSECTING MANUAL. 



parts; the third sacral divides into upper and lower parts. 

 The anterior parts of the lumbar nerves unite in one trunk, and 

 the posterior parts in another, which together form the lumbo- 

 sacral cord. The posterior parts of the lumbar and first two 

 sacral nerves form the peroneal nerve; the anterior parts of 

 the same nerves, together with the upper part of the third sa- 

 cral, form the tibial nerve. [647] 



PUDENDAL PLEXUS. 



This lies on the back wall of the pelvis and is formed by 

 fibres from the first three sacral nerves, and all the fourth and 

 fifth sacral and the coccygeal. A visceral branch (white ramus 

 communicans) runs from the third (and second or fourth) 

 sacral to the pelvic plexus and viscera. The perforating cuta- 

 neous nerve arises from the back of the second and third sacral 

 and runs through the great sacro-sciatic ligament to the but- 

 tock. Muscular branches, from the loop between the third and 

 fourth sacral, supply the Levator ani, Coccygeus, and External 

 sphincter; offsets from the branch to the latter supply the 

 skin on the ischio-rectal fossa and fold of the nates behind 

 the anus. The anterior sacro-coccygeal nerves are the descend- 

 ing branches of the fourth and fifth sacral and the coccygeal ; 

 they form a plexus (coccygeal) beside the coccyx, and twigs 

 from this run through the great sacro-sciatic ligament to the 

 skin near the coccyx. The other branches of the pudendal 

 plexus are the small sciatic and the pudic. [655-658] 



Small Sciatic. Springing from the back part of the first 

 three sacral nerves at the junction of the sacral and pudendal 

 plexuses, this runs through the great sciatic notch, below the 

 Pyriformis, to the thigh. Its perineal branch (inferior puden- 

 dal) arises at the lower border of the Gluteus maximus, runs 

 inward over the hamstrings and below the ischial tuberosity, 

 becomes subcutaneous over the pubic arch, and supplies the 

 skin on the scrotum and root of the penis (labium majus and 



[202] 



