Chap, xiv.] NERVE-FIBRES. in 



tricus) shows such divisions to an extraordinary degree, 

 one huge nerve-fibre dividing at once into a bundle of 

 minor fibres. Division of a medullated fibre takes 

 place generally at a node of Ranvier. The branches 

 taken together are generally thicker than the un- 

 divided part of the fibre, but in structure they are iden- 

 tical with the latter. 



146. When medullated nerve-fibres approach their 

 peripheral termination, they change sooner or later, in 

 so far as their medullary sheath suddenly ceases ; and 

 now we have a non-medullated, or Remak's nerve- 

 fibre. Each of these consists of an axis cylinder, a 

 neurilemma, and between the two a nucleated nerve 

 corpuscle from place to place. Non-medullated nerve- 

 fibres always show the fibrillar nature of their 

 axis cylinder. The olfactory nerve-branches are 

 entirely made up of non-medullated nerve fibres. In 

 the branches of the sympathetic most fibres are non- 

 medullated. 



The non-medullated fibres undergo always repeated 

 divisions. They form plexuses, large fibres branching 

 into smaller ones, and these again joining (Fig. 68). 

 Generally at the nodal points of these plexuses there are 

 triangular nuclei, indicating the corpuscles of the 

 neurilemma. 



147. Finally the non-medullated nerve-fibres lose 

 their neurilemma, and then we have simple axis 

 cylinders. These branch and ultimately break up 

 into the constituent primitive nerve-fibrillce, which 

 occasionally show regular varicosities (Fig. 69). 

 Of course, of a neurilemma or the nuclei of the 

 nerve corpuscles there is nothing left. These 

 primitive fibrillse branch and anastomose with one 

 another, and thus form a network. The density 

 of this network depends on the number of primitive 

 fibrils and the richness of their branching. These 

 primitive fibrils and their networks represent the 



