Central nervous system of Tunica nigra. 123 
places, while still others penetrated more or less into the cortex 
of the ganglion (Figs. G, J, K). 
Apparently the central cells are chiefly for association. The 
fibers from the ones on the surface are undoubtedly to a large 
degree efferent, the processes for the most part passing through the 
center of the ganglion on their way to the larger nerve branches. 
A few large cells, however, at the periphery, as stated, appear to 
send their fibers out more directly to muscles. Cells at the edge 
of, as well as just inside, the more compact mass bring various 
levels of the ganglion into relation with each other. (Fig. G is a 
somewhat diagrammatic plan of the ganglion as seen in cross section.) 
The cells shown are in the actual relations as found in different 
sections, but the efferent and afferent fibers are represented as 
though prolonged into the nerve trunk, in the plane of a single 
section, which is a condition not generally realized. Not so many 
direct communications were found between cells and the nerve 
trunks, although many individual neurons could be seen to send 
their strands in towards the center of the ganglion and in some 
cases direct communications were found. In other words, efferent 
fibers usually run first to the center of the ganglion and then, after 
a longer or shorter longitudinal course take exit through the nerve 
trunks. Receptive cells at the surface of the body, possibly similar 
to those described by Hunter (1898a), probably send their processes 
into the ganglion and may be in some degree related to the central 
cells. I think it probable that there are not many of these pro- 
cesses aS compared with the efferent fibers. 
The relations of cells to each other. 
In a few rather doubtful cases larger processes of neurons were 
seen to join with other nerve cells (Fig. K). With specimens stained 
in iron-hematoxylin after fixation in Fremming’s fluid, as well as 
with some of the other material, it was often possible to trace the 
branches from cortical nerve cells for considerable distances into 
the depths of the ganglion. In favorable localities these processes 
were seen to branch and the delicate branches were followed some- 
times as far as, and apparently became continuous with, similar 
delicate fibers of other cells. The minute twigs were often as fine 
as the fibrillae which were made out in some of the larger neurons, and 
seemed to be continuous with the fibrillae within the larger processes 
