THK NERVE-MUSCLE PREPARATION 



21 



ovaries and oviducts or testes, bladder. Cut through the lower end of the rectum 

 and through its attached mesentery. On raising it, two elongated red bodies 

 the kidneys are seen at the back of the abdomen, partly covering the nerves 

 which are passing down to the hind limbs. Remove the kidneys without touching 

 the nerves. Now hold the frog up by its legs so that the viscera hang towards the 

 head, and cut through the lower end of the vertebral column with strong scissors 

 so as to separate the fore part of the trunk and the viscera from the pelvis and 

 hind limbs. Lay the latter preparation on a clean glass plate or on a piece of 

 paraffined paper on the frog-cork. Note the several muscles which are seen on 

 the front and back of the lower limbs (figs. 28, 29). The gastrocnemius is gener- 

 ally used for experiments. Tie a thread round its tendon (tendo Achillis), and 



Hiac ext. 



Tensor fasc. lat. 



Triceps fern. 



1'yriformia. 



Seruimembranosus. Iliofibula. 



Peroneus. 



Tibial ant. long. 



Tendo Achillis. 



I *i* /!KAiA 



Tars. ant. 



FIG. 28. MUSCLES OF FROG-LEG : DORSAL ASPECT (GUupp). 



cut this away from the calcaneum. Holding it by the thread, tear the muscle 

 upwards away from the tibia, and sever this bone just below the knee. 



Next bring to view the sciatic nerve. Separate the muscles at the back of 

 the thigh by the aid of two pairs of forceps, keeping to the mesial of the two 

 chief intermuscular septa, and the nerve will be seen, accompanied by the 

 femoral vessels. On no account touch the nerve, but separate the muscles from 

 it so as to expose it freely. 



If only a short piece of nerve is required, a wet thread may be tied round the 

 uppermost end of the length of nerve displayed, and the nerve may be cut 

 across above the thread. Then, holding it up gently by the thread and passing 

 a pair of straight scissors below and parallel to the nerve, its branches to the 

 thigh muscles are successively severed, and the nerve is separated as far as the 

 back of the knee-joint. Notice that as each branch is snipped the muscles which 

 it supplies contract. Lay the nerve thus isolated upon the gastrocnemius muscle. 

 Then cut through the middle of the femur, and clear the attachments of the 

 thigh muscles away from the lower end of that bone. You now have a prepara- 



