i8o 



PRACTICAL PHYSIOLOGY. 



[xxx. 



incision through the skin along the back of one thigh — say the left 

 — from the knee to the lower end of the coccyx, and prolong the 

 incision along the hack a httle to tlie left of the urostyle. Reflect 

 the skin, and expose the muscles shown in fig. 105. 



(b.) Gently separate the semi-membranosus and biceps with the 

 *' seeker," and bring into view the sciatic nerve and femoral vessels. 

 Some use a glass rod drawn to a thin prolonged point, instead of a 

 " seeker." Still working with the seeker and beginning near tlie 

 knee, clear the sciatic nerve, but do not scratch or stretch the nerve, 

 or touch it with forceps. Divide the pyriformis and iho-coccygeus, 

 and trace the nerve up to the vertebral column. 



(r.) Divide the spinal column above the seventh lumbar vertebra ; 

 seize the tip of tlie urostyle with forceps, raise it, and with the strong 

 scissors cut it clear from all its connections as far as the last lumbar 

 vertebra, and then divide the urostyle itself. Divide the left ihac 

 bone above and below, and remove it with the muscles attached to 

 it. The lumbar plexus now comes into view. Bisect lengthways 

 the three lower vertebrae, and use the quadrilateral piece of bone 

 by which to manipulate the nerve. AVith forceps lift the fragment 

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

 to the knee, dividing any branches with 

 fine scissors. Keep the parts moist with 

 normal saline. 



(d.) Divide the skin over the gastroc- 

 nemius, and expose this muscle. Divide 

 the tendo Achillis below its fibro-cartilage, 

 lift the tendon with forceps and detach the 

 gastrocnemius 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 

 j\ 11 injury, clear the muscles away from the 



lt\ ^^ lower end of the femur, and then divide the 



femur itself about its middle. This prepara- 

 tion (fig. 107) consists of the gastrocnemius, 

 and the whole length of the sciatic nerve, 

 to which is attached a fragment of bone, 

 by which the preparation can be manipulated 

 without injuring the nerve. 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. 



(B) (a.) Another metliod is sometimes adopted. Destroy a frog's brain 

 and 82)inal cord. With the left hand seize the hind limbs and hold the frog 



Fig. 107. — Nerve - >ruscle 

 Preparation. S. Sciatic 

 nerve — the fragment of 

 the spinal column is 

 not shown ; F. Femur ; 

 and /. Tendo Achillis. 



