22i ELEMENTAEY BIOLOGY. [XIII. 



a. The sciatic nerve. 



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

 rating the biceps and semimembranosus mus- 

 cles ; 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. 



7. Follow it up to the abdominal cavity, cutting 

 away the muscles, lying between the ilium and 

 urostyle, which cover it in. 



S. 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 {pero- 

 neal) between its two heads. 



&t 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 

 gastrocnemdus, enters that muscle. 



/3. Follow the nerve down the leg : it nms along 

 the tibiahs posticus muscle, giving off branches 

 here and there. 



ly... 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. 



