cl NERVOUS SYSTEM. 



the dark borders of the fibre, is very conspicuous. This is sometimes 

 considered to be only the primitive sheath of the fibre modified in character, 



Fig. LXXXV. 



Fig. LXXXV. SMALL BRANCH OP A MUSCULAR NERVE OP THE FROG, NEAR ITS TERMI- 

 NATION, SHOWING DIVISIONS OP THE FlBRES. 



a, into two ; b, into three ; magnified 350 diameters. (From Kolliker. ) 



but it seems more probable that it is derived from the neurilemma or peri- 

 neurium which incloses the fine bundles or funiculi, and, as these part into 

 smaller collections and single fibres, undergoes a corresponding division, aud 

 finally sends sheaths along single fibres. 



In further treating of the terminations of nerves, it will be convenient to consider 

 the sensory and motor nerves separately. 



Of the sensory, or, at least, non-muscular nerves, the following modes of final dis- 

 tribution have been recognised. 



A. By networks, or terminal plexuses. These are formed by the branching and 

 inter] unction of the pale fibres above described. The meshes of the net may be at 

 first wider, and the threads, or bundles of threads, larger, but from these, finer fila- 

 ments forming closer reticulations proceed, and then sometimes the nuclei become 

 less frequent, or disappear. Such networks are found in the skin of the frog, rat, and 

 mouse; in various parts of the mucous membranes, in the cornea, and also in the 

 connective tissue beneath serous membranes or between their layers in different parts 

 of which the mesentery of the frog affords a good example. In some of these cases 

 the nerve-fibres come into the vicinity of connective-tissue-corpuscles, but, so far as I 

 have been able to see, are not connected with them. 



B. Sensory terminal organs. Three varieties of these are now recognised, viz., 

 a., end-bulbs b., touch-corpuscles, and c., Pacinian bodies. These have so far a 

 common structure, that in all of them there is an inward part or core (Innenkolben 

 Germ. ) of soft, translucent, finely granular matter ; an outer capsule of ordinary connec- 

 tive tissue with its pertaining corpuscles ; and, finally, one or sometimes more nerve- 

 fibres, pale and without dark contours, which pass into the core and apparently end 

 with a free, usually somewhat swollen, or knobbed extremity. Thus agreeing in 

 their internal and probably essential structure, the terminal organs differ chiefly, or 

 at least most obviously, in their capsule, which, simple in the end-bulbs, becomes 



