STRUCTURE OF NERVE-CELLS. 321 



Cells of this kind are mefc with occasionally in the sympathetic ganglia both of the 

 frog (where they were first discovered by Beale) and of the mammal. 



In multi-polar cells either one or more of the cell-processes may be prolonged 

 into nerve-fibres. In the large ramified nerve-cells of the anterior comu of the 

 spinal cord only one of the many processes is prolonged into a nerve-fibre. This is 

 known as the axis-cylinder process of Deiters (figs. 372, 373, a), and is distinguished 

 from the other processes of the cell by being unbranched and of a somewhat clearer 

 and more evenly fibrillated appearance than the other processes, which branch again 

 and again, becoming finer as they proceed, until they are eventually lost to sight in 

 the grey matter. 



The ramified cell-processes have been regarded by Golgi as representing rootlets by means 

 of which the cells penetrate into and derive nutriment from the surrounding grey matter^ 

 With this idea he has termed them the " protoplasmic " processes as distinguished from the 

 nerve-fibre process or processes. Although there does not seem to be sufficient evidence in 

 favour of this view ; and the intimate relationship which obtains between the ramified pro- 

 cesses of different nerve-cells may still be considered to point to these processes as a means of 

 transmission and diffusion of nerve impulses in the grey matter, the view which was formerly 

 entertained that the ramified processes are united with one another into a network pervading 

 the grey matter is not substantiated by the employment of the most recent methods of 

 research, although these methods permit of the following out of the processes of a nerve-cell 

 to a much greater extent than any that had been previously in use. In all cases the processes 

 appear to end after a number of branchings in free terminations : the branchings may be 

 closely interlaced with those of neighbouring cells, but to all appearance remain anatomically 

 distinct from them. 



The axis-cylinder process of a nerve-cell is distinguishable from the other pro- 

 cesses not only in the fact that as a rule it does not, like those, undergo a dendritic 

 ramification near the cell from which it takes origin, but also, as was shown by Golgi, 

 in giving off, at right angles to its course, minute lateral fibrils at frequent intervals 

 (fig. 369, a). These lateral fibrils lose themselves in the surrounding nervous matter ; 

 they perhaps come into relation with similar fibrils from other cells or from nerve- 

 fibres, but both their actual mode of termination and their functional significance 

 are at present unknown. According to Flechsig they become medullated. 



Ultimately even the axis-cylinder processes of the nerve-cells undergo dendritic 

 ramification. This is seen in the terminal ramification which is the usual mode of 

 ending of both motor and sensory nerve-fibres, and in the ramification of branches 

 from the posterior root-fibres in the grey matter of the spinal cord (see fig. 383, p. 328). 

 .Sometimes this ramification of the axis-cylinder process occurs nearer to the body of 

 the cell, as in the case of the cells of the outer layer of grey matter of the cerebellum, 

 in which the axis-cylinder processes, after a longer or shorter course, break up into 

 one or more close dendritic ramifications which envelope the cell-bodies of the 

 corpuscles of Purkinje (fig. 375). 



Some multi-polar cells, many of those in the ganglia for instance, possess two, 

 three, or more nerve-fibre processes and no protoplasmic processes (fig. 367). 

 Sometimes these axis-cylinder processes of a nerve-cell, especially those in the 

 sympathetic, are continued along their whole course as pale nerve-fibres. But in 

 most cases, at a short distance from the body of the cell, they acquire a medullary 

 sheath and become in fact medullated nerve-fibres (fig. 373, a'). In the bi-polar 

 cells (those at least of a pyriform shape), the one fibre may be prolonged as a pale 

 fibre, the other may be a medullated fibre. In other instances both fibres may be 

 medullated or non-medullated. In multi-polar cells of the sympathetic ganglia one 

 process may be continuous with one of the small medullated fibres which enter these 

 ganglia, and the others with non-medullated fibres which pass from the ganglia to 

 the peripheral distribution of the nerves. In this manner the cells may act as 

 distributing centres multiplying the paths of the nervous impulses towards the 



