252 EXPERIMENTAL PHYSIOLOGY. 



upper and lower ends of this incision, short incisions are made across 

 the limb and the skin flap is reflected forward. At the upper end 

 of the exposed wound the lower edge of the relatively small gluteus 

 maximus muscle is made out (a small vein running along its lower 

 border) and is cut at its lower end and reflected upward. It is now 

 possible by retracting the muscles between which it lies to separate 

 the sciatic nerve and to make out a large branch passing backwards 

 from it. This is the hamstring nerve and it is cut. The sciatic 

 nerve is next followed downwards to where the two divisions of the 

 trunk (peroneal and tibial) diverge. A ligature is tied around the 

 nerve at this point, the nerves cut distal to the ligature and their 

 central ends placed in Sherrington's electrodes. It will be noted 

 that the above nerve sections render practically all muscles in the 

 thigh incapable of reflex contraction except the extensor muscles. 



It is now necessary to arrange for graphic records of movements 

 at the knee joint. For this purpose the leg is amputated near the 

 ankle joint. After tying a stout mass ligature (threaded by a pack 

 needle through the skin and muscles around the stump so as to hold 

 it in place) a thread is also attached to the skin of the stump, and con- 

 nected with a suitable muscle lever, using pulleys if necessary. 

 The femur must also be immobilized at its lower end so that the 

 knee joint may be held in a flexed position and the slightest move- 

 ment at this joint recorded without disturbance by any other move- 

 ments of the preparation. For this purpose it is necessary to 

 insert a threaded steel pin into the condyles of the femur on their 

 median aspect. To insert the drill pin, an ordinary drill, procurable 

 at any hardware shop, is used. The drill head is unscrewed from 

 the pin after this has been screwed into the bones and a brass rod, 

 threaded at one end so that it fits the thread of the screw pin, is 

 connected to the pin with its outer end held by a clamp to an up- 

 right stand. 



These preliminary operations being completed, the preparation 

 is placed on its right side, and the femur of the left thigh arranged 

 so that it is supported by the drill pin and brass rod in a nearly 

 vertical position, with the hips flexed almost to a right angle. 

 In cases in which the decerebrate rigidity is marked, the left knee 

 will be nearly extended. If it is not so, it may be placed in this 

 position by passive extension (the shortening reaction what does 

 it depend on?) 



