NERVE-MUSCLE PREPARATION. 



149 



clearly into view. Bisect lengthways the three lower ver- 

 tebrse, and use the quadrilateral piece of bone by which to 

 manipulate the nerve. With the forceps lift the fragment 

 of bone, and with it the sciatic nerve ; trace the latter down- 

 wards to the knee, dividing any connections and branches 

 with fine scissors. If the parts tend to become dry, moisten 

 the whole preparation with normal saline solution. 



(d.) Divide the skin over the gastro- 

 cnemius, and expose this muscle. 

 Divide the tendo achillis below its 

 fibre-cartilage, lift the tendon with a 

 pair of forceps, and detach the gastro- 

 cnemius from its connections as far up 

 as the lower end of the femur. Cut 

 across the knee-joint, and remove the 

 tibia and fibula with their attached 

 muscles. Taking care to preserve the 

 sciatic nerve from injury, clear the 

 muscles away from the lower end of 

 the femur, and then divide, with the 

 large pair of scissors, the femur itself 

 about its middle. This preparation 

 (Fig. 52) consists, therefore, of the 

 gastrocnemius, and the whole length 

 of the sciatic nerve, to which is at- 

 tached a fragment of bone, by which 

 the preparation can be manipulated 

 without injuring the nerve. 



Fig. 52. Nerve-muscle 

 Preparation. S, Sci- 

 atic nerve the frag- 

 ment of the spinal 

 column is not shown ; 

 F, femur ; and I, tendo 

 achillis. 



N.B. The nerve must not be touched with instruments, 

 neither stretched nor scratched, nor allowed to come into contact 

 with the skin, and it must be kept moist with normal saline. 



(a.) Another method is sometimes adopted. Pith a frog. 

 With the left hand seize the hind limbs and hold the frog 

 with its belly downwards. With one blade of a sharp- 

 pointed pair of scissors transfix the body immediately 

 behind the shoulder-blades, and divide the spinal column. 

 The head now hangs down, and by its weight it pulls the 

 ventral from the dorsal parts. 



(6.) With the scissors divide the wall of the abdomen on 

 both sides parallel to the vertebral column, and remove all 



