216 ANATOMY FOE, NUKSES. [CHAP. XVIII. 



in the gray matter of the brain, in the spinal cord, and in vari- 

 ous ganglia ; their termination, or peripheral distribution, is not 

 so easy to determine. 



All nerves, medullated or non-medullated alike, in approaching 

 their final distribution, divide ; that is, the numerous strands or 

 fibres which go to make up a nerve separate from one another. 

 If we follow a fibre, we find, if it is a medullated one, that the 



FIG. 126. SECTION OF SKIN SHOWING TACTILE CORPUSCLE IN PAPILLA, d, 

 nerve passing up to tactile corpuscle ; t, tactile corpuscle. 



sheaths enclosing it gradually disappear, and finally the axis 

 cylinder itself splits into its component fibrils. These fibrils 

 may terminate in invisible threads, as between the cells in the 

 Malpighian layer of epidermis, or they may terminate in special 

 end organs, such as the tactile bodies in the papillae of the 

 skin, the round-end bulbs in the conjunctiva, the motorial rami- 

 fications in the muscular fibres, and in other ways too numerous 

 and too complicated for us to attempt to describe. 



Degeneration and regeneration of nerves- The divided ends of a 

 nerve that has been cut across readily reunite by cicatricial tissue, that is 

 to say, the connective tissue framework unites, but the cut ends of the 

 fibres themselves do not unite. On the contrary, the peripheral or severed 

 portion of the nerve begins to degenerate, the medullary sheath breaks up 

 into a mass of fatty molecules and is gradually absorbed, and finally the 



