EFFECT OF THE LIMB ON GROWTH OF NERVE FIBERS 



147 



Effect of the limb on 

 growth of nerve fibers 



The optic nerve, which has a preformed pathway between the retina and 

 the brain, has no difficulty in finding its way, and needs no direction to reach 

 its normal destination. But how are we to explain the development of the 

 sensory and motor nerves supplying the muscles of the back and the limbs ? 



NORMAL limb AND NERVES 



TRANSPLANT LIMB POSTERIORLY 



10 9 8 7 6 



NORMAL NERVES OlRECTEO TO TRANSPLANT 



Fig. 86. The directional effect of the limb upon the third, fourth, and fifth 

 spinal nerves. Top: Nerves 3, 4, and 5 normally grow toward the forelimb. 

 Center: The forelimb is transplanted in a slightly posterior position. Bottom: 

 Nerves 3, 4, and 5 turn posteriorly and innervate the displaced limb. 



