THE SPINAL CORD 2 3 



There are two varieties of neuraxons which were first distinguished by Golgi. These 

 differ in their course and destination. (i) From some cells the neuraxon proceeds in a long 

 course, giving off collaterals, but preserving its identity till it reaches its destination. It may 

 end in another distant part of the nervous system; or in a muscle, which it reaches by way 

 of the motor nerve trunk; or in the skin which it reaches by way of a sensory nerve; 

 or in some organ of the body. When a cell has such a long neuraxon, it is brought into 

 relation, by means of it, with some distant and different part of the body. It is such a 

 neuraxon which proceeds from the cells of the anterior horns of the cord, enters the nerve 

 root, and goes to the muscles, forming a motor nerve fibre. It is such a neuraxon which 

 proceeds from the Clarke column of cells in the base of the posterior horn, and ascending 

 the cord, in the direct cerebellar column, ends in the cerebellum. Golgi classed all cells 

 with such long neuraxons together as his "first type" of cells. He affirms that all such 

 cells are of motor function, but this hypothesis is no longer accepted. This type of cells is 

 easily recognized. It is shown, e.g., in Plates IV. and V. in the spinal cord and in Plates 

 XL II. and XLIII. in the cerebral cortex. 



(2) There is a second kind of neuraxon which has a short course and divides and sub- 

 divides soon after leaving the cell, thus forming a plexus of fine fibres in the gray matter, 

 and never proceeding in any particular direction to a great distance. Golgi classes cells pos- 

 sessing this form of neuraxon together as a " second type" An example of this type is shown 

 in Plates XLV. and XLVI. He affirms that they are sensory cells; that the neuraxons and 

 their branches from such cells unite with one another, forming a fine network or plexus of 

 fibres, and he states that the sensory nerve fibres arise from or terminate in this network. It 

 has been shown, however, by Cajal that no such true network exists. It is known, further, that 

 cells with such neuraxons are to be found in all parts of the nervous system, not particularly in 

 the posterior horns of the cord ; hence the sensory character of this type of cell is now denied. 

 No essential functional distinction between cells of the first and second type can as yet be admitted. 

 Cajal has shown that the sensory fibres do not join any such network as Golgi describes, but 

 end in free extremities, and he considers these cells of Golgi's second type as having a sort of 

 associative function. There is but one neuraxon to each cell throughout the nervous system. 



The usual termination of the neuraxon in the nervous system is by breaking up into sev- 

 eral fine filaments, forming a terminal brush, each filament ending freely with or without 

 a little terminal knob. Such a termination has already been shown in Plate V. The col- 

 laterals also have free ends with brush-like expansions. Thus the cell preserves its identity 

 in its neuraxon as in its dendrites. It has a wide possibility of distribution of its impulses 

 through the neuraxon, but it never comes into direct continuity with another cell. 



