430 THE NERVOUS SYSTEM. 
and thus form sub-groups more or less perfectly marked off from each other. This is most 
evident in the cervical and lumbar swellings of the cord, where, in conformity with the 
large anterior nerve-roots which issue from the cord, the ventral cells are much more 
numerous than in the dorsal region, and where also certain of the motor cells are especially 
large in conformity with the great length of the efferent fibres which proceed from them. 
for the supply of the distant muscles of the limbs. 
Two such sub-groups of the ventral cells are easily recognised, viz. a mesial and a 
lateral. The mesial group occupies the inner or mesial part igh the anterior gray horn, 
whilst the lateral group occupies the outer part of the anterior gray horn. In the cervical 
and lumbar enlargements of the cord the cells of the lateral group increase greatly in 
number and become massed together in two collections, viz. a set in front called the 
ventro-lateral sub-group, and a set behind and more deeply placed, which receives the 
name of the dorso-lateral sub-group. 
It is thought by some that this grouping of the ventral column of cells stands in rela- 
tion to the muscle-groups to which their axis cylinder processes are distributed. 
Lateral Cell-Column.—In those regions of the cord where the lateral horn 
of gray matter is well marked a group of cells may be seen within it. In other 
districts of the cord the same cell-group may be detected, although it is not so 
distinctly represented. 
Posterior Vesicular Column—Clarke’s Column.—This occupies the posterior 
horn of gray matter and is the most conspicuous of all the cell-groups in the 
cord. It does not, however, extend along the whole length of the cord; imdeed 
it is almost entirely confined to the dorsal region, and in consequence it is some- 
times referred to as the “dorsal nucleus.” Above, it begins opposite the seventh or 
eighth cervical nerve, whilst below, it may be traced to the level of the second 
lumbar nerve, Where it disappears. In transverse section of the cord it presents an 
oval outline, and is seen in the inner part of the cervix of the posterior horn of 
gray matter immediately behind the gray commissure (Fig. B). On the outer side 
it is circumscribed by numerous curved fibres from the entering posterior nerve- 
root, and in the lower dorsal region of the cord (opposite the eleventh and twelfth 
dorsal nerves) it becomes so marked that it forms a bulging on the inner aspect 
of the posterior gray horn. 
The cells of Clarke’s column are large, and possess several dendritic processes. 
The axons enter the lateral column of white matter and there form a strand of 
fibres, which will later on be described under the name of the direct cerebellar 
tract. 
In addition to the topographical subdivision of the nerve-cells of the cord indicated above, it 
is now usual to classify them according to the nature of the axons which proceed from them. 
Thus we have (1) the cells of Golgi or cells w ith short axons, and (2) cells with long axons. 
The cells of Golgi possess axons which do not emerge from the gray matter, but bring neigh- 
bouring cells into touch with each other. The cells with long axons are of two kinds, VIZ. 
radicular cells and strand-cells. 
The radicular cells are those from which the axon emerges from the cord in the shape of an 
efferent nerve-fibre. Thus the “motor cells” which supply the axis cylinder processes of the 
anterior nerve-roots belong to this class. The strand-cells are those which contribute their axons 
to the formation of those fibres which form certain of the strands or tracts which are found in 
the white matter of the cord. 
Nerve-fibres in the Gray Matter of the Cord —Nerve-fibres both of the 
medullated and non-medullated variety pervade every part of the gray matter. 
They are of three kinds, viz. (1) collaterals, (2) terminations of nerve-fibres, (3) 
axons given off by the cells. The nerve-fibres which compose the columns of white 
matter of the cord give off numerous fine collateral branches, which pass into the 
gray matter from all sides and finally end in relation with the nerve-cells. The 
majority of the nerve-fibres themselves, which thus give off collaterals, finally turn 
in and enter the gray matter, to end similarly. As already noted, the axons of the 
cells in the case of the cells of Golgi remain within the gray matter, but all the 
others emerge either for the purpose of entering a peripheral nerve or for the pur- 
pose of entering a strand of fibres in the white “atter of the cord. 
The nerve-fibres thus derived are interwoven together in the gray matter of the 
cord in a dense inextricable interlacement. 
