37 
NERYE-CELLS IN THE MAMMALIAN SPINAL-CORD. 
fibres. That these distant cells are to be considered as belonging to the group of the 
lateral horn is to be inferred from the similarity of them to those in shape and size. 
They are of oval figure, with the long axis in the transverse plane of the cord. They 
are of the same size as, or slightly larger than, the lateral horn-cells. Five of them, 
taken without selection, measured respectively 32, 30, 34, 33, and 29 p,, giving the 
average of 31'6 p. Five cells taken from the lateral cornu in the same prepara¬ 
tions measured respectively 30, 35, 26, 28, and 31 p, giving an average for the five of 
30 p. They are, moreover, arranged wuth their long axes ujDon lines which radiate 
backwards and outwards from the lateral cornu, suggesting a common o]’igin from 
that point (fig. 4, Plate 3). They appear to be more numerous in the Human cord 
than in the other of the cords examined. The vertical fibres of the white matter 
in which they lie embedded belong to the area of the lateral column, called by 
Flechsig the lateral limiting layer ; but it may well be that those lying furthest out 
are beyond this layer, and within the area of the crossed pyramidal tract. The 
arrangement of the cells in the transverse plane, and the coincidence of the longer 
axis of the cell-body with the direction of the medullated fibres running horizontally 
in the same connective tissue septa as contain the cells, suggest, however, that the 
cells are connected with the horizontal fibres radiating between the grey matter and 
the white column, rather than with the vertical fibres of the column. But the hori¬ 
zontal fibres must be in turn continuous with certain of the vertical; with which of 
these, however, is a question that at present there is no possibility of deciding. 
To the dorsal side of the lateral horn, and often continuous with it, e.g., in the 
lower part of the cervical enlargement, is the processus reticularis. It merges dorsally 
in the lateral portion of the cervix and caput cornu dorsalis. In the bars of its 
reticulum made up of many interlacing horizontally and vertically running bands of 
fibres, numerous ganglion cells exist. For the most part, the cells seem attached to 
those bands of the interlacement which are horizontal. They present more variety of 
form than do the previously mentioned groups, and they seem to be equally numerous 
upon frontally running, and upon sagitally running bands of the formation. Many 
are small and fusiform, and many are somewhat larger and triangular. The triangular 
cells resemble closely the cells above-described in the bands of the white commissure, 
and likened by Schiefeerdecker* to arrow-heads in their shape. The cells of the 
reticularis may, one must imagine, be related to the numerous small ganglion cells, 
chietly fusiform, but often triangular, which occupy the grey matter bordering on the 
processus. These, as Clarke stated,! lie for the most part with their length parallel 
to the nearest portion of free edge of the grey substance, except that the deeper lying 
of them_ are mostly directed outward, as if belonging to continuations of the cross¬ 
running transverse fibres of the commissures. These cells point into the bars of 
extension of the grey matter which form the roots of the processus reticularis, and 
* Loc . cit . 
t Loc . cit . 
