NERVES. 



[ 639 ] 



NERVES. 



small end of the bell-shaped ganglion-cells 

 of the sympathetic in the frog, and that 

 whilst one pursues a straight course, the 



Fig. 514. 



Cells from the central grey substance of the human 

 spinal marrow. Some are connective-tissue cells. 

 Magnified 350 diameters. 



other forms a series of coils around it, both 

 lying within a nucleated sheath continuous 

 with that of the ganglion-cell. 



Origin of Nerve-fibres. The ganglion- 

 cells, whether multipolar or unipolar, are in 

 continuity with nerve-fibres. Some gan- 

 glion-cells are merely nucleated dilatations 

 of the axis-cylinder ; and others, which are 

 also bipolar, are true ganglion-cells; for the 

 more or less globular cell-mass is continuous 

 with the axis-cylinder and with the granu- 

 lar matter of the medullary matter, but the 

 tubular sheath of the nerve stops short of 

 the cell. 



Multipolar ganglion-cells are invariably 

 connected with one medullated nerve-fibre, 

 which passes off without branching or 

 diminishing in calibre. Its axis-cylinder is 

 continuous with the fibrillar structure of the 

 protoplasm of the ganglion-cell, and it be- 

 comes invested with the medullary sheath 

 soon after leaving the cell. The other pro- 

 cesses either communicate with adjacent 

 multipolar cells, or break up after repeated 

 branching into a great number of processes, 

 which,however, are clearly continuous with 

 the fibrillar protoplasm of the cell, but are 

 uncovered by any medullary sheath. Their 

 ultimate termination is doubtful ; but it is 

 inferred that many of them become continu- 

 ous with the axis-cylinders of nerves. So 



Fig. 515. 



Large cells from the grey cortical layer of the human cerebellum. Magnified 350 diameters. 



fibrillar are the processes under reagents, 

 and so fibrous is the appearance of the gan- 

 glion cell-mass, deficient as it is of cell-wall, 



that it is imagined that the fibrous structure 

 of the axis-cylinders is continuous with that 

 of each other through the cell-substance. 



