866 THE NERVOUS SYSTEM. 



found to vary ; together, they supply all the toes excepting the outer side of the 

 little toe and the adjoining sides of the great and second toes, the former being 

 supplied by the external saphenous, and the latter by the internal branch of the 

 anterior tibia!. 



Surgical Anatomy. The lumbar plexus passes through the Psoas muscle, and, therefore 

 in psoas abscess any or all of its branches may be irritated, causing severe pain in the part to 

 which the irritated nerves are distributed. The genito-crural nerve is the one which is most 

 frequently implicated. This nerve is also of importance, as it is concerned in one of the princi- 

 pal reflexes employed in the investigation of diseases of the spine. If the skin over the inner 

 side of the thigh just below Poupart's ligament, the part supplied by the crural branch of the 

 genito-crural nerve, be gently tickled in a male child, the testicle will be noticed to be drawn 

 upward through the action of the Cremaster muscle, supplied by the genital branch of the same 

 nerve. The same result may sometimes be noticed in adults, and can almost always be produced 

 by severe stimulation. This reflex, when present, shows that the portion of the cord from which 

 the first and second lumbar nerves are derived is in a normal condition. 



The anterior crural nerve is in danger of being injured in fractures of the true pelvis, since 

 the fracture most commonly takes place through the horizontal minus of the os pubis, at or 

 near the point where this nerve crosses the bone. It is also liable to be injured in fractures and 

 dislocations of the femur, and is likely to be pressed upon and its functions impaired in some 

 tumors growing in the pelvis. Moreover, on account of its superficial position it is exposed to 

 injury in wounds and stabs in the groin. When this nerve is paralyzed, there is loss of motion 

 in the Iliacus, in the Quadriceps extensor cruris, in the Sartorius, and partial paralysis of the 

 Pectineus. There is loss of sensation down the front and inner side of the thigh, except in that 

 part supplied by the crural branch of the genito-crural and by the ilio-inguinal, as well as down 

 the inner side of the leg and foot as far as the ball of the great toe. 



The obturator nerve is of special surgical interest. It is rarely paralyzed alone, but occa- 

 sionally in association with the anterior crural. The principal interest attached to it is in con- 

 nection with its supply to the knee, pain in the knee being symptomatic of many diseases in 

 which the trunk of this nerve or one of its branches is irritated. Thus it is well known that in 

 the earlier stages of hip-joint disease the patient does not complain of pain in that articulation, 

 but on the inner side of the knee or in the knee-joint itself. Again, the same thing occurs in 

 sacro-iliac disease. The obturator nerve is in close relationship with the sacro-iliac articulation, 

 passing over it, and, according to some anatomists, distributing filaments to it. Again, in cancer 

 of the sigmoid flexure, and even in cases where masses of hardened faeces are impacted in this 

 portion of the gut, pain is complained of in the knee. Finally, pain in the knee forms an 

 important diagnostic sign in obturator hernia. The hernial protrusion as it passes out through 

 the opening in the obturator membrane presses upon the nerve and causes pain in the parts sup- 

 plied by its peripheral filaments. When the obturator nerve is paralyzed, the patient is unable 

 to press his knees together or to cross one leg over the other, on account of paralysis of the 

 Adductor muscles. Kotation outward of the thigh is impaired from paralysis of the Obturator 

 externus. 



The great sciatic nerve is liable to be pressed upon by various forms of pelvic tumors grow- 

 ing from the pelvic viscera or bones, by aneurisms of some of the branches of the internal iliac 

 artery, calculus in the bladder when of large size, accumulation of faeces in the rectum, giving 

 rise to pain along its trunk, to which the term sciatica is applied. Outside the pelvis exposure 

 to cold, violent movements of the hip-joint, exostoses or other tumors growing from the margin 

 of the sacro-sciatic foramen, may also give rise to the same condition. When paralyzed there 

 is loss of motion in all the muscles below the knee, and loss of sensation in the regions sup- 

 plied by it. 



The sciatic nerve has been frequently cut down upon and stretched for the relief of sciatica, 

 and also in cases of locomotor ataxy, the anaesthesia of leprosy, etc. In order to define it on 

 the surface, a point is taken at the junction of the middle and lower third of a line stretching 

 from the posterior superior spine of the ilium to the outer part of the tuber ischii, and a line 

 drawn from this to the middle of the upper part of the popliteal space. The operation of 

 stretching the sciatic nerve is performed by making an incision over the course of the nerve 

 about the centre of the thigh. The overlying structures having been divided, the interval 

 between the inner and outer'hamstrings is to be defined, and these muscles pulled inward and 

 outward with retractors. The nerve will be found a little to the inner side of the Biceps. It 

 is to be separated, hooked up with the finger, and stretched by steady and continuous traction 

 for two or three minutes. The sciatic nerve may also be stretched by what is known as the 

 " dry " plan. The patient is laid on his back, the foot is extended, the leg flexed on the thigh, 

 and the thigh strongly flexed on the abdomen. While the thigh is maintained in this position 

 the leg is forcibly extended to its full extent and the foot as fully flexed on the leg. 



The position of the external popliteal, close behind the tendon of the Biceps on the outer 

 side of the ham, should be remembered in subcutaneous division of the tendon. 



