TKE SPINAL COED IN MAN, MAMMALIA, AND BIEDS. 
929 
which separated in succession from the rest to be connected with one of the nerve-cells. 
Fig. 26, Plate XL VII. is an exact representation of a thick fibre giving off a short 
branch, which immediately subdivided into two and perhaps other fine filaments, to join 
a corresponding number of cells. The lower and broken end of the fibre seemed to be 
split up into its constituent parts, and resembled the hairs of a brush. Very frequently 
a series of pyriform cells, in close apposition, but one in advance of the other, were 
arranged in a compact group around a common fibre, with a fibril of which each was 
connected by its tapering end. Fig. 27 represents part of such a group, magnified 
420 diameters. The connecting fibrils were of different lengths, and sometimes so short 
that the small end of the cell seemed to arise from the fibre itself. Where the relative 
position of the cells forming a compact group is less regular, we have the appearance 
represented in fig. 28. Through such a group the nerve-fibres pursue a more or less 
tortuous course, giving off branches or their component fibrils in succession, and in all 
directions, to the cells between which they pass. In fig. 29, for example, a fibre, after 
giving off fibrils to be connected with the smaller ends of the two uppermost cells, con- 
tinued its course between them to be connected by a fibril with the next cell, along 
the sides of which two other branches ran in a similar way until they reached the points 
of other cells ; and so on in different directions and planes. Between the upper and 
lower ends of the figure the cells were broken off, and exposed the fibre and its short 
branches. 
When separated from the group, a large number of the cells seemed to have scarcely 
any investment that might be called a distinct cell-wall ; but still they were frequently 
more or less covered by a shaggy layer of delicate fibres (a, a!, fig. 30, Plate XLVIII.), by 
which in their natural position they appeared to be connected. This investment seemed 
to be an extension from the surface of the fibres or processes with which the cells were 
continuous, and occasionally entangled a small nucleus (a!, fig. 30). In some instances, 
as at h, it assumed the appearance of a thin, loose, and delicate sheath ; while in others, 
as at c, it formed a more compact investment, to which the nuclei were more closely 
adherent. 
As development progressed the cells somewhat enlarged, while their walls increased 
in thickness, and, like the nerv'e-fibres, were studded with an increasing number of small 
nuclei. Fig. 31, Plate XLVIII. shows a portion of one of the intervertebral ganglia of 
a foetal sheep, 8 inches long, magnified 420 diameters. Many of the cells, which had a 
globular appearance in their natural positions, were found to be pyriform when separated 
by dissection. Their walls were evidently prolongations from the surfaces of the nerve- 
fibres ; the nuclei on the former were in every respect similar to those on the latter ; and 
in both cases their number increased in the same proportion. Sometimes a nucleus was 
found at the point where a fibre was continuous with a cell ; so that it was impossible to 
say whether it belonged to the one or the other. Fig. 32 represents a group of cells 
from the anterior part of an intervertebral ganglion of the chick, on the ninth day of incu- 
bation, at the point where the nerve-fibres are escaping to join the anterior roots. The 
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