318 



THE SPINAL NERVES. 



externus and in front of the adductor brevis, but behind the pectineus and adductor 

 longus muscles. It gives branches as follows : 



(a) An articular branch to the hip-joint arises in the thyroid foramen. 



(ft). Muscular branches are given to the gracilis and adductor longus muscles, and 

 generally also to the adductor brevis. 



(c) The terminal twig turns outwards upon the femoral artery, and surrounds 

 that vessel with small filaments. 



(d) An offset at the lower border of the adductor longus communicates beneath 

 the sartorius with the internal cutaneous branch of the anterior crural nerve, and 

 with a branch of the internal saphenous nerve, forming a sort of plexus. 



B. The posterior or deep part of the obturator nerve, having perforated the upper 



Fig. 207. THE LUMBAR PLEXUS FROM BEFORE. WITH THE 



DISTRIBUTION OF SOME OF ITS NERVES. (Slightly 



altered from Schmidt.) i 



, last rib ; b, quadratus lumborum muscle ; c, 

 oblique and ti-ansverse muscles, cut near the crest of 

 the iliimi and turned down : d, pubis ; c, adductor 

 brevis muscle ; /, pectineus divided and turned out- 

 wards ; <j. adductor longus ; 1, ilio-hypogastric nerve ; 

 2, ilio-inguinal ; 3, external cutaneous ; 4, anterior 

 crural ; 5, accessory obturator ; 6, obturator, united 

 with the accessory by a loop round the pubis ; 7, genito- 

 crural in two branches cut short near their origin \ 

 8, 8, lumbar portion of the gangliated' sympathetic 

 cord. 



fibres of the obturator externus muscle,, 

 crosses behind the short adductor to the fore- 

 part of the adductor magnus, where it divides 

 into several branches, all of which end in 

 those muscles, excepting one which is pro- 

 longed downwards to the knee-joint. 



(a) The muscular branches supply the 

 external obturator and the great adductor 

 muscle, with the short adductor also when 

 this muscle receives no branch from the 

 anterior division of the nerve. 



(b) The articular branch for the knee 

 rests at first on the adductor magnus, but 

 perforates the lower fibres of that muscle,, 

 and thus reaches the upper part of the 



popliteal space. Supported by the popliteal artery, and sending filaments around 

 that vessel, the nerve then descends to the back of the knee-joint, and enters the 

 articulation through the posterior ligament. This branch is often wanting. 



Varieties. The obturator nerve sometimes has an additional root from the first or the 

 fifth lumbar nerve. In extreme cases of the hig-h form of the plexus it may arise from the- 

 upper three lumbar nerves. The root from the second nerve is rarely wanting- (Eisler). It 

 occasionally gives a branch to the pectineus muscle. A branch to the obturator internus is 

 described by Krause. Eisler traced filaments to the obturator artery and the periosteum on 

 the back of the pubis. 



Occasional cutaneous nerve. In some instances the communicating 1 branch described 

 above is larg-er than usual, and descends along- the posterior border of the sartorius to the 

 inner side of the knee, where it perforates the fascia, communicates with the internal 

 saphenous nerve, and extends down the inner side of the limb, supplying' the skin as low as 

 the middle of the leg 1 . 



When this cutaneous branch of the obturator nerve is present, the internal cutaneous 

 branch of the anterior crural nerve is small, the size of the two nerves bearing an inverse 

 proportion to each other. 



