THE SPINAL COED IN MAN, MAMMALIA, AND BIEDS. 
919 
increased in diameter ; while those of the posterior grey substance, as far forward as the 
posterior level of the canal, had scarcely, if at all, advanced in size. In all the darker 
parts of the latter they were still very closely aggregated, but less so than in fig. 3 ; so 
that the network of fibres by which they were connected was conspicuous in a corre- 
sponding proportion. Fig. 10, Plate XLV., represents some of the nuclei and their 
connecting fibres, from the arched layer {Ih) of the posterior cornu in fig. 4, magnified 
670 diameters*. In the section, however, although it was exceedingly thin, the nuclei 
were rather more crowded in that part ; but exactly the same appearance is presented 
where a very thin portion has been shaved to an edge. 
Throughout the whole of the anterior grey substance the average size of the nuclei 
is about twice as great as in the posterior grey substance, and therefore about twice as 
great as in every part of section 3. Their increase in diameter begins rather abruptly 
near the posterior level of the oval canal. They have also become more granular, more 
distinctly circumscribed by well-defined walls, and lie at greater distances from each 
other. The tissue which supports them has still a reticular structure, but is looser, 
more open, and in the central portion of the cornu consists of a sponge-like network of 
coarser fibres, which are more or less granular and connected with the nuclei by irre- 
gular aggregations of granules. Fig. 12, at v, Plate XL VII., is a faithful representation 
of this peculiar arrangement, which can be more intelligibly represented than described. 
In the middle of the cornu, where it is traversed by the central fibres of the anterior 
nerve-roots, as they run directly backward, the structure has very much the appearance 
delineated in fig. 11, Plate XLYII. But in the antero-lateral parts of the cornu (w, w\ 
figs. 4 7, Plate XLV.), where the groups of large nerve-cells are developed, it has a 
kind of honeycomb arrangement in the form of circular or somewhat irregular cavities 
or cells, which are large, but variable in diameter, and frequently in close apposition, 
but often separated by angular interspaces containing each a nucleus encrusted with 
granules. Fig. 12, x x, Plate XLVII. is a very exact representation of a portion of the 
outer or lateral group (w', fig. 7, Plate XLV.). The walls of the cavities and the gra- 
nular network are directly connected with the tissue of the antero-lateral white columns 
at y, y. Within each cavity is a nucleus, which is sometimes in or near the centre, 
sometimes more excentric, and sometimes close to the wall. The nucleus is imbedded 
in granules, which are generally seen to connect it to the wall, and which in some 
instances occupy the whole, in others only part of the cell ; in the latter cases they 
aggregate in a variety of forms f. 
Within the posterior angle or shoulder of the anterior cornu is a remarkable dark 
and nearly triangular group of nuclei (fig. 4, f, Plate XLV.), which difier from the rest 
only in being rather larger, and more closely aggregated. 
The roots of the nerves may be very distinctly traced into the grey substance (see 
* By some mistake this figure is marked in the Plate as X 420 diameters. 
t The separation of the granular masses from their cell-walls, and the stellate form which they sometimes 
assume, seem due to the action of the chromic acid. 
MDCCCLXII. 6 K 
