xrii.] THE FROG. 733 



a. The sciatic nerve. 



a. Find it on the dorsal side of the thigh by 

 separating the biceps and semimembranosus 

 muscles ; it appears as a slender white cord. 



/?. Dissect it out carefully in the middle of the 

 thigh, noting the branches it gives off to the 

 various muscles. 



y. Follow it up to the abdominal cavity, cutting 

 away the tissues lying between the ilium and 

 urostyle, which cover it in. 



8. Follow it down towards the knee : a little 

 way above the joint it divides into two 

 branches; one (posterior tibial] runs inside 

 the large head of the gastrocnemius muscle, 

 the other (peroneal) between its two heads. 



b. The posterior tibial nerve. 



a. Note especially the branch which it gives off 

 opposite the knee-joint, and which, after run- 

 ning for some way along the deep surface of 

 the gastrocnemius, enters that muscle. 



ft. Follow the nerve down the leg : it runs along 

 the tibialis posticus muscle, giving off branches 

 here and there. 



y. Near the foot it turns to the back of the 

 ankle-joint and enters the plantar surface 

 of the foot, where it ends in a number of 

 branches. 



c. The peroneal nerve. 



a. This runs down the leg close to the peroneus 

 muscle, giving off branches on its way. 



