NERVE-CELLS IN THE MAMMALIAN SPINAL-CORD. 
39 
Out-lying Ganglion-Cells in the Fosterior Column. 
As in the antero-lateral, so also in the posterior column of the cord out-lying gang¬ 
lion-cells exist. And it would seem that the anatomy of the out-lying cells in the 
posterior column is less complex than that of the former classes. In the first place, 
the cells appear to be confined to one portion of the posterior column, namely, the 
extero-posterior division of it, and in that division to one particular area, namely, the 
radicular zone. In the second place, one has obtained definite evidence of their 
existence from a certain region only of the length of the cord, namely, from that 
which is especially characterised by the large dimensions assumed by the posterior 
vesicular column of Clarke. 
The out-lying cells appear to be situated in the root-zone exclusively upon certain of 
the horizontal radiations of the root-fibres from the white column into the grey cornu. 
These radiations are among those which in transverse sections through tlie cord can 
be seen to pass from the dorso-median limit of the root-zone in a ventral and lateral 
direction to enter the grey substance in the neighbourhood of Clarke’s column, often 
describing as they do so bold curves with the convexity turned toward the postero¬ 
median fissure. They are radiations consisting of root-fibres, which belong to the 
median division in Krause’s* classification of the bundles of the dorsal roots. They 
enter the grey matter without previously passing through any part of the mesial limb 
of the gelatinous substance. BeghterewI has shown that they are composed of fibres 
which already are possessed of the medullary sheath in the human foetus of 25 cm. 
length, and are therefore among the earliest of the fibres of the cord to be developed. 
It is also to be remembered that their fibres are among those of largest calibre in the 
whole of the dorsal spinal nerve-root. 
The form of the out-lying cells found in these radiations of the dorsal root may'be 
described as oval (figs. 6, 7, 8, Plate 4) ; one end is usually considerably the less 
pointed. A nucleus, which is large and contains a very obvious nucleolus, is fairly cen¬ 
trally placed within the cell, though often somewhat nearer the blunter of the two 
extremities. The cells have not been observed isolated in teased preparations, but 
they may really be of a more symmetrically bipolar figure than the foregoing descrip¬ 
tion would suggest. Although they are certainly chiefly extended in the plane at 
right angles to the long axis of the cord, a very slight inclination in such a plane, 
either of themselves or of the section in which they lie, would suffice to truncate one 
end of the spindle-shaped cell-body. In such a case the nucleus, if centrally placed, 
would appear nearer to the more rounded pole. That this does actually happen and 
frequently explains the somewhat unipolar appearance of the cell, is suggested by the 
fact that the more pointed end, continued into an obvious cell-process, is sometimes 
turned with the fibres of the dorsal root in the direction of the grey substance of the 
* ‘ Allgemeine u. Mikroskop. Anatomie,’ 1876, p. 389. 
t ‘ Arcliiv f. Anat. ii. Pliysiol., Anat. Abth.,’ 1887, p. 126. 
