48 



EXPERIMENTAL GENERAL PHYSIOLOGY 



3. Operation. To make a gastrocnemius "muscle-nerve prep- 

 aration." 



(1) Make, with scissors, a circular cutaneous incision around the 

 tarsus, corresponding with the lower end of cut B. Make a longi- 

 tudinal cutaneous incision, beginning at the margin of the circular 

 incision where it crosses the external aspect of the tarsus, carry it 

 along the tibia, along the course of the biceps femoris muscle, over 

 the pyriformis to the posterior end of the urostyle, along the whole 

 extent of the urostyle. From the posterior end of the urostyle make 

 an incision posteriorly and ventrally, for 1 cm. or 2 cm. Grasp the 

 free margin of the skin at the point of the circular incision and with 

 a quick traction toward the head of the frog the skin will be removed 

 from the whole field of operation. 



FIG. 28 



A, a glass nerve hook; B, the classic muscle-nerve preparation. 



(2) Pass a point of the fine scissors under the glistening tendon 

 of the biceps femoris where it is inserted into the tibia, taking care 

 not to injure any of the neighboring tissues. Sever the tendon. 

 Grasp its free end; lift the biceps up, carefully cutting the delicate 

 connective tissue which joins it to neighboring structures; sever 

 its heads. The removal of the biceps and a separation of the cleft 

 which the biceps occupied reveals three bloodvessels and the large 

 trunk of the sciatic nerve. Which of the bloodvessels is the sciatic 

 artery? Which is the sciatic vein? Which is the femoral vein? 



(3) Grasp and lift up the posterior end of the urostyle, sever the 

 iliococcygeal muscles, remove the urostyle. 



The sciatic plexuses formed by the seventh, eighth, and ninth 

 pairs of spinal nerves will be revealed. 



(4) Pass a glass nerve hook under the sciatic nerve; gently lift it 

 up, severing, with the scissors, the connective tissue. The pyriformis 

 muscle must also be divided. The whole length of the sciatic nerve 



