THE SYMPATHETIC SYSTEM OF NERVES. 1353 



between the greater trochanter and the tuberosity of the ischium above to the middle of 

 the popUteal space below. At about the junction of the middle and lower thirds of 

 the thigh it divides into the internal and external popliteal nerves. Below the gluteus 

 maximus muscle it is comparatively superlicial, so that tenderness of the nerve, as 

 from sciatica, is easily elicited by pressure. At the point where it emerges from 

 under the gluteus maximus it is readily reached for operation. After a vertical in- 

 cision through the skin and fascia at this level, the biceps muscle is exposed. The 

 lower margin of the gluteus maximus is raised and the biceps drawn inward, when 

 the nerve can be easily hooked up with the finger. Because of the great importance 

 of this nerve to the lower extremity it is not advisable to excise or divide it as this 

 would paralyze its whole area below. Stretching is the only justifiable operation, 

 although the results obtained are often disappointing, and the operation may cause 

 acute neuritis. According to Trombetta, it will require a tension equal to the weight 

 of 183 lbs. to break it, and it is more likely to yield at its attachment to the spinal 

 cord than elsewhere. It should, therefore, tolerate a stretching force of from 100 to 

 160 lbs. (Treves). A safe working rule is to use a force sufhcient to raise .the 

 affected limb from the table, the patient lying in the prone position. 



It has been observed that when the paralysis is due to some pressure upon the 

 nerves of the sacral plexus within the peh'is it is often confined to the peroneal or ex- 

 ternal popliteal 7ierve, or is most marked in it. This has been explained by the fact 

 that the fibres for the peroneal nerve lie close together directly on the pelvic bones, 

 and are, therefore, particularly exposed to pressure. They arise for the most part 

 from the lumbo-sacral cord, formed by the fourth and fifth lumbar and first sacral 

 nerves, which lie directly on the innominate crest, the rest of the plexus lying on the 

 pyriformis muscle. 



In paralysis of the external popliteal or peroneal nerve the extensors of the foot 

 and toes, the tibialis anticus and the peronei muscles are involved. The foot hangs 

 down from its own weight (foot drop), and turns in from paralysis of the peronei. 

 In some cases the anterior tibial muscle escapes. In walking the knee must be un- 

 duly flexed to prevent the toes from dragging on the ground and the arch of the foot 

 is flattened from the loss of the support given to the arch by the peroneus longus. 

 If sensation is disturbed it will be only to a slight extent over the anterior part of the 

 leg about the shin, and outward from this on the dorsum of the foot and toes, but not 

 at the sides of the foot. The peroneal nerve may be divided accidentally in a sub- 

 cutaneous tenotomy of the biceps tendon for contraction at the knee, the nerve lying 

 close to the inner border of the tendon. It may be injured by external violence, as 

 it passes around the head and neck of the fibula, where if necessary, an incision will 

 easily expose it ; or it may be injured by pressure, as in prolonged kneeling. 



In paralysis of the internal popliteal 7ierve all the other muscles of the leg, in- 

 cluding the superficial and deep flexors, the tibialis posticus, the plantar muscles and 

 interossei are affected. The patient cannot extend the ankle and therefore cannot 

 stand on his toes. The toes cannot be flexed or moved sideways. Sensation is dis- 

 turbed on the inner and posterior surface of the leg, the outer border of the foot, the 

 sole and the plantar surface of the toes. 



In paralysis of the entire sciatic nerve the flexors of the knee also are involved, 

 so that the patient cannot bring the heel toward the buttock. If only one sciatic is 

 involved he can still walk by fixing the knee in extension, the whole limb being- 

 brought forward by the quadriceps extensor, which is supplied by the anterior crural 

 nerve, 



THE SYMPATHETIC SYSTEM OF NERVES. 



The sympathetic portion (systema nervorum sympatheticum) of the peripheral 

 nervous system differs from that already described — the spinal and the cranial nerves 

 — in being particularly concerned in carrying efferent and afferent impulses to and 

 from the thoracic and abdominal organs (collectively termed the splaiichnic area), 

 in contrast to the great somatic fskeletal) masses of voluntary muscle. Whilst the 

 paths for the afferent or sensory impulses conducted from the splanchnic area differ 

 in no important respect from those formed by the cerebro-spinal nerves, the efferent 

 or motor paths are peculiar (a) in supplying the involuntary and cardiac muscle and 



