8o Journal of Comparative Nf.urologv. 



the periphery of the body and here constitute the peripheral end- 

 organ (sensory or motor apparatus). The termini of the motor 

 nerves on the muscles, for instance, would belong to this cate- 

 gory. We have thus a simple type of a neurone in the motor 

 cells of the anterior horns of the spinal cord, together with the 

 fibres of the anterior roots which spring from them, pass to the 

 muscle, and here in the motor end plate break up into a term- 

 inal brush. 



With reference to the peripheral sensory apparatus, a differ- 

 ent relation seems possible. For many nerve fibres which serve 

 the sensory functions we must assume that the cells from which 

 the nerves originate (in this case not central ganglion cells, but 

 peripheral sensory cells) are in the peripheral sense-organs ; e. g. 

 the olfactory cells of the epithelium of Schneider's membrane, 

 or perhaps the fibres arising from the rods and cones of the 

 retina — in short, this relation seems to be the rule, or nearly so, 

 for the nerves of the higher senses, the so-called nerves of special 

 sense. But most sensory fibres, those especially which serve the 

 sense of touch with its subordinates, pressure, temperature, and 

 others, seem to end free at the periphery after they have here 

 branched out into their terminal brushes. 



Having spoken in detail of those structural units which to- 

 gether make up the whole nervous system — the nerve units, or 

 neurones — and having seen that the most recent investigations 

 furnish us with many new views with reference to them, we may 

 proceed to discuss briefly how far our previous ideas of the 

 structure of the nervous system must be modified in view of 

 these facts. 



First, I repeat that many of the more recent investigators 

 proceed on the view that the neurones correspond throughout to 

 the scheme previously explained ; i. e. that no nerve fibres 

 pass directly into a nerve cell at both ends and that no ganglion 

 cell has more than one axis-cylinder springing from it. Permit 

 me, however, to state distinctly that neither of these positions 

 seems to me conclusively proven. 



In discussing the connection of every neurone with the rest 

 of the nervous system, as well as with the organism as a whole, 

 the question hinges on the relations of the terminal brush. 

 Here three possibilities must be considered. 



