192 THE NED VOUS SYSTEM. 



the N. coccygeus over the M. illo-coccyyeun to join this nerve at the 

 point marked Com. The twig cc behaves in like manner after re- 

 ceiving a twig from h. The twig h arises from the inner surface of 

 the ninth nerve between the two foregoing and close to its union 

 with the eighth spinal nerve ; from this origin twig h passes almost 

 transversely outwards to the hinder extremity of the oviduct 

 (" uterus ■'•'), and partly to the rectum, crossing in its course twig a, 

 the sciatic nerve, and the urostyle. Its branches form a net- 

 like plexus with the terminal branches of the last sympathetic 

 ganglion and with a branch cc from the point of union Com. 



' A second branch (a), arising from the point of junction Cow, is 

 a continuation of the JV. coccygeus (Mio) ; it passes vertically down- 

 wards towards the hinder end of the cloaca and at the upper border 

 of the Levator ani, divides into two branches, which are distributed 

 to the inner and outer surfaces of this muscle and to the cloaca. 

 Other branches pass dorsally to the lymph-hearts, while a third set 

 pass to the hindermost part of the bladder. 



' These three sets of nerves, to the M. coccygen-^, M. levator ani, 

 and to the lymph-hearts, are not supplied entirely by the N. coccy- 

 geus, as this is reinforced by one or more branches (e) from the 

 sciatic plexus : this branch [e) supplies twigs to the il/, ilio-coccygeus, 

 which is also supplied anteriorly from the trunk of the i\'^ coccygeals. 



' The bladder receives a special branch {fl), which arises from the 

 sciatic plexus at the junction of the eighth and ninth spinal nerves ; 

 this nerve gives a twig [d') to the M. iliacns.' 



I. The sciatic nerve (^Y. isc/iiadieus) (Fig. 128 /) is the largest 

 nerve of the body; it passes under the M. coccygeus, between the 

 origins of the IF. vastus externus and of the A[. pyramid alls : lies then 

 between the il/, biceps and the M. 2^yramidaHs, and later between the 

 M. bicepjs and the M. setnimembranosus ; lastly, it bifurcates under 

 the 31. biceps to form the N'. tibialis (II) and the N. pero?ieus (///). 

 In this coiirse it gives off : — 



(a) A twig to the 31. coccygeo-iliacus, while still in the pelvis, 



{b) The N. cutaneiis femoris posterior (Fig. 128, 3), which passes be- 

 tween the M. pyramidalis and the M. vastus externus, to appear behind 

 and beneath the former ; it accompanies an artery of like name to 

 supply the skin of the hinder and inner surfaces of the thigh. 



{c) A little below the foregoing it gives off a collateral branch 

 (Fig. 128, 3), which passes under the 31. pyramidalis and divides to 

 form — 



