THE L UMBOS A CRAL TR UNK 



1005 



than usual, and it then descends, along the dorsal border of the sartorius, to the medial side of the 

 knee, where it enters the subcutaneous tissue, and, proceeding downward, supplies the skin 

 on the medial side of the leg as far as the middle of the calf. Twigs join it with the saphenous. 



The posterior branch of the obturator (fig. 767) pierces the upper part of the 

 obturator externus and passes downward between the adductor brevis and addu c- 

 tormagnus. Its branches are: — 



1. Muscular branches to the obturator externus, to the obUque fibres of the adductor magnua 

 and to the adductor brevis when the latter is not entirety suppHed by the anterior branch. 

 The branch to the obturator externus is given off in the obturator canal. 



2. An articular branch to the knee-joint which appears in some cases to be the continuation 

 of the trunk of the posterior branch (fig. 767). It either pierces the lower part of the adductor 



Fig. 768. — Distribution of Cutaxeous Nerves ox the Posterior and Axterior Aspects 



OF THE Inferior Extremity. 



Last thoracic 



Anastomotic 

 branch of 

 peroneal 



Sural 



Middle clunial 



Inferior medial 

 clunial 



nio-ingulnal' 



Medial 

 calcaneal 

 branches 

 of tibial 



Superficial 

 peroneal 



Lateral dorsal 

 cutaneous 



Deep peroneal 



magnus, or it passes through the opening for the femoral artery. In the popliteal space it 

 descends on the popUteal artery to the back of the joint, where it pierces the posterior Hgament, 

 and its terminal filaments are distributed to the crucial ligaments and the structures in their 

 immediate neighbourhood . This branch is not uncommonly absent. Occasionally the posterior 

 branch of the obturator nerve also supples a twig to the hip-joint. 



The accessory obturator nerve arises from the third or fourth or from the third and fourth 

 lumbar nerves, in the angles between the roots of the femoral (anterior crural) and obturator 

 nerves. It is present in about twenty-nine per cent, of all cases (Eisler). It is often closely 

 associated with the obturator nerve to the level of the brim of the pelvis, but instead of passing 

 through the obturator foramen, it descends along the medial border of the psoas, crosses the 

 anterior part of the brim of the pelvis, passes beneath the pectineus, and terminates in three 

 main branches. One of these branches joins the anterior division of the obturator nerve, 

 another supplies the pectineus, and the third is distributed to the hip-joint. 



The Lumbo-sacral Trunk 



The trunk of the plexus usually formed by the union of the smaller part of 

 the fourth and the entire fifth lumbar nerves is called the lumbo-sacral trunk 



