112 



THE PHYSIOLOGY OF NERVE 



but are interwoven with neighboring branches, into an intricate net- 

 work or plexus. When the individual nerve-fibers reach the end- 

 organ, they subdivide into finer threads, or fibrils. In the vicinity of 

 the end-organ the investing membranes disappear. 



Fig. 64. — A, nerve fibers stained with osmic acid, showing axis cylinder, medullary 

 sheath and neurolemma; B, medullated nerve fiber, showing nodes of Ranvier; X 660 

 times. (Schdfer.) 



The thickness of nerve-fibers varies between less than 2/x and more than 20/x. 

 Those innervating the skeletal muscles are large and possess a diameter of about 

 14-1 9)U. While these differences are due very largely to the fact that some nerve- 

 fibers are devoid of a medullary sheath, it must be remembered that even the axis- 

 cylinders vary greatly in their thickness. Thus, it is easily apparent that the axons 

 arising from the large ganglion cells of the anterior horn of the spinal cord, possess 

 an especially large caliber. Nerve-fibers are either medullated or non-medullated 



