THE SPINAL NERVES. 191 



the coeeyg"eal nerve immediately beyond the Canalis coccygeus^ 

 perforates the M. ilio-coccygeus, and runs on its dorsal surface 

 obliquely over the lymph-heart, without supplying- it; the nerve 

 then pierces the fascia to supply the skin of the back and thigh. 



[e) The Bamus ahâomhialis also arises from the coccygeal nerve ; 

 it is larger than the B. dorsalis, and arises at the same poiat ; the 

 nerve runs on the ventral surface of the M. ilio-coccf/yens towards the 

 lymph-heart, and inosculates with the sympathetic. It is from this 

 nerve that the branch to the sciatic plexus is iTsually given off ; it 

 further supplies a varying- number of branches, which with branches 

 derived directly or indirectly from the sciatic nerve, form a plexus 

 (Plexus coccygeufi) ; the two plexuses may together be regarded as a 

 Plexus iscJiio-coccjjgetts or a Plexus sacro-cocci/geus. 



[f) In addition to the 7?^;/?'" communicantes given off by the spinal 

 nerves near the vertebral column, the sciatic plexus supplies a few 

 twigs, usually two (Fig*. 127). 



[g) Other small twigs pass from the sympathetic system for- 

 wards and outwards to join the sciatic plexus or the sciatic nerve. 

 According to Waldeyer two of these are very constant. 



(//) Branches to the oviduct (Fig. 127 h). 



(i) Branches to the rectum (Fig. 127 cr). 



(^) Branches to the bladder (Fig. 127 d). 



(/) Branches to the 31. levator ani (Fig-. 127 a). 



(;;;) A branch to the lymph-heart, which runs along the anterior 

 border of the M. lev. ani, on to its dorsal surface, and then direct to 

 the lymph-heart. 



Variations in the sciatic plexus. The arrangement of the 

 nerves in the sciatic plexus is subject to many variations ; ac- 

 cording to Wiedersheim most of these variations belong to two 

 chief classes : either the N. coccygeiis inosculates directly with the 

 ninth spinal nerve by one or several branches, or it joins the ninth 

 nerve indirectly by uniting with its branches. A case of the 

 latter arrangement is seen in Fig. 127, and is thus described by 

 Wiedersheim : — 



' After cutting through the pelvic symphysis and dravvnng to one 

 side the contained viscera, namely, the hinder end of the oviduct, 

 the rectum, and the bladder, one sees a row of small twigs (a, h, 

 cc, d, and e) arising from the inner, hinder, and anterior surfaces of 

 the ninth spinal nerve : the first [a) runs backwards parallel with 



