THE ANTERIOR CRURAL NERVE. 319 



Accessory obturator nerve. This slender nerve is pi'esent in one out of every three or 

 four bodies (29 per cent., Eisler). It arises from the third and fourth lumbar nerves (rarely 

 also from the fifth, sometimes only from the third), between the roots of the obturator and 

 anterior crural nerves, bein^- associated at its origin more closely with the latter, but it is often 

 bound up for a short distance with the obturator nerve, of which it then appears to be a 

 branch. It descends beneath the iliac fascia along- the inner border of the psoas muscle, 

 crosses over the superior ramus of the pubis, and passing behind the pectineus muscle, ends by 

 dividing into branches. Of these, one joins the superficial part of the obturator nerve ; another 

 enters the pectineus on its under surface : and a third passes to the hip-joint. Throug-h the 

 communication with the obturator nerve fibres may also pass to the adductor long-us, gracilis, 

 and adductor brevis muscles, rarely to the skin of the inner side of the thi^h. The accessory 

 nerve is sometimes very small, and ends in filaments which perforate the capsule of the joint. 

 (See A. M. Paterson, ''The pectineus muscle and its nerve-supply," Journ. Anat., xxvi, 1891, 

 and op. cit. ,v., Journ. Anat., xxviii, 95 ; P. Eisler. " Der Plexus lumbosacralis," 1892). 



SUMMARY. The obturator nerve and accessory obturator supply the three 

 adductor muscles of the thigh, with the gracilis and obturator externus, and in 

 some cases, the pectineus. They also give branches to the hip and knee-joints; and 

 occasionally a cutaneous branch descends to the inner side of the thigh, and to the 

 inner and upper part of the leg. 



Anterior crural or femoral nerve. This, the largest nerve arising from 

 the lumbar plexus, is derived principally from the third and fourth lumbar nerves, 

 but in part also from the second and first. Emerging from the outer border of the 

 psoas muscle near its lower part, it descends into the thigh in the groove between 

 that muscle and the iliacus, and therefore to the outer side of the femoral blood- 

 vessels. Below Pouparb's ligament, the nerve becomes flattened out and divides into 

 two parts, one of which is mainly cutaneous, while the other is distributed for the 

 most part to muscles. 



A. Branches in the trwik. The branches given from the anterior crural nerve 

 within the abdomen are few and of small size. 



(a) The iliacus receives three or four small branches (2, 3 I), which are directed 

 outwards from the nerve to the muscle. 



( b) The nerve of the femoral artery is a small branch which divides into numerous 

 filaments upon the upper part of that vessel. It sometimes arises lower down than 

 usual, in the thigh. It may, on the other hand, be found to take origin above the 

 ordinary position from the third lumbar nerve. Beck and Rauber describe 

 filament passing from this nerve, in company with the medullary artery, to the 

 femur. 



B. Terminal branches. From the principal or terminal divisions of the nerve 

 the remaining branches take their rise as follows. 



From the superficial or anterior division cutaneous branches are given to the 

 fore part of the thigh, and to the inner side of the leg ; they are the middle and 

 internal cutaneous nerves. Two muscles, the sartorius and the pectineus, receive 

 their nerves from this group. 



From the deep or posterior division branches proceed to supply the extensor 

 muscle of the knee, and also one cutaneous nerve, the internal saphenous. 



(a) Middle cutaneous nerve. The middle cutaneous nerve ( 2, 3 /) either pierces the 

 fascia lata in two parts about four inches below Poupart's ligament, or as one trunk 

 which soon divides into two branches. These branches descend on the fore part of 

 the thigh to the front and inner side of the patella. After or before the nerve has 

 become subcutaneous, it communicates with the crural branch of the genito-crural 

 nerve, and also with the internal cutaneous. 



This nerve, or the outermost of its branches, frequently pierces the upper part of 

 the sartorius muscle. 



(b) Internal cutaneous nerve. The internal cutaneous nerve (2, 3 /) gives branches 



x 2 



