88 JouRNAL OF CoMPARATIVE NEUROLOGY. 
of the nucleus the tigroid-bodies are usually triangular in out- 
line, and some of them have a very considerable size. Tigroids 
are found far out in the dendrites, assuming here a lenticular 
or even a linear form, their long axes parallel with the course 
of the dendrite, A finely granular axone-hillock lies at the 
origin of the axone. In rectangular cells, as the one figured, 
the hillock may be spread so widely as to assume a disk-like 
form. The tigroids tend to become somewhat smaller in the 
region of the hillock. 
The tract-neurones are not demonstrated readily with either 
chrome-silver impregnation or the intra-vitam injection of meth- 
ylen-blue. The homogeneous coloration assumed by some of 
them with Nisst staining has already been recorded. The char- 
acter of such micro-chemical reactions indicates clearly that 
many of these neurones are not physiologically active, at least 
not all of the time. “The axones from some of them may enter 
the motor root of one of the anterior spinal nerves, and, being 
in an active condition, give indications of it in a well-marked 
store of tigroid substance. - Other neurones, however, chaining 
together higher and lower levels of the oblongata, have come 
to have their functions largely usurped by the development of 
more specialized tracts. Such neurones are, therefore, degraded 
to a far lower plane of metabolic activity, and they respond but © 
feebly to those of our stains which depend upon the presence 
of definite chemical constituents of the protoplasm. 
b. Commissural Neurones.—The commissural neurones are 
readily distinguishable from the tract-neurones by their smaller 
size (Fig. 2, c. z.). Commissural neurones have a wide distri- 
bution. They are scattered between the tract-neurones in the 
vicinity of the median raphe, and they also are to be found in 
all parts of the lateral region as far dorsal as the base of the 
general cutaneous nucleus. 
The external morphology of a commissural neurone is rep- 
resented in Fig. 3, c. x. The cell-body is relatively small in 
proportion to the extension of the dendrites and the axone. 
The form of the cell is usually an elongated oval or an irreg- 
ular triangle. The dendrites are quite often only two in num- 
=" 
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a a 
