110 EXERCISE XVIII 



Arrange the recording-drum so that its direction of rotation is such that 

 the horizontal rod carried below it on the same spindle will knock open the 

 lever of the primary circuit-key when that is set. The direction is preferably 

 from right to left when viewed from in front. The speed of translation of the 

 recording- surface should be not less than 25 cm. a second (i. e. with ordinary 

 sized drum about one revolution in 2 sees., with the larger Palmer drum 

 about one revolution in 4 sees.). 



See that a strong thread, of sufficient length, is securely attached to the 

 short arm of the belt-crank lever. 



Electrodes : the ordinary hand-electrodes, but fixed to the end of a piece 

 of small lead-tubing (e. g. 5 mm. diameter), the lead's other end soldered to an 

 inch or so of brass rod, for clamping to a standard. This flexible holder 

 allows the electrodes to be set and left in any position the nerve-stump in the 

 wound may require. » 



CDetermine, by attaching the wires from the secondary coil to a small 

 galvanometer and noting the direction of the needle deflection when the key 

 in the primary circuit is opened, which of the electrodes is the kathode for 

 the break-induced current, and mark that electrode by tying a cotton to it.] 



COr the glass-tube electrodes (PI. IX, fig. 5) may be preferred as keeping 

 nerve better warm and moist : with these a standard is required carrying a 

 horizontal arm, a piece of stick with a split end of adjustable height for 

 supporting the weight of the double flex wire which will connect the 

 electrodes with the bridge-key of the secondary circuit.] 



See that the drill (text-fig. 38) and 2 drill-pins and the brass rods and 

 heavy standards for holding them are at hand. 



III. i. Operation. Place preparation supine, with neck-stump and 

 fore-quarters turned somewhat to the right. Attach clip-weight to each hind- 

 foot and put limbs in an extended position. Attach a heavy clip-weight to 

 skin of front of left knee to keep the knee somewhat abducted (the operation 

 posture is indicated in PI. IX, fig. 6). 



III. ii. At a point in the left inguinal flexure. well lateral to the mid- 

 point of the groin, commence a skin incision 5 cm. long running lengthwise 

 down the thigh and then curving parallel with but below the fold of the 

 groin. The inguinal pad of subcutaneous fat is exposed : reflect this upward 

 with the skin. Note the position of the femoral vein and artery ; about 

 8 mm. lateral to the latter the lower end of ilio-psoas muscle is seen, and 

 emerging from it the femoral nerve. The nerve and muscle are to be cut 

 across somewhat above Poupart's ligament, care being taken to avoid the 

 iliac vein, which is separated from ilio-psoas only by the thin tendon of the 



