ME. J. L. CLAEKE ON THE INTIMATE STETJCTUEE OE THE BEAIN. 
265 
projects into tlie restiform body (c) and constitutes its grey nucleus, or tbe restiform 
ganglion. In figs. 4 & 5, we find the same changes carried to a still greater extent. In 
the latter the decussating bundles of the anterior pyramids come only from the central 
grey substance and roots of the anterior cornua at the sides of the canal, and scarcely at 
all, as they did in fig. 4, from the lateral columns (d 1 ), in which now the original net- 
work is again distinguishable ; but it is larger, closer, more beautiful than we found it 
in fig, 1, and contains in its meshes bundles that have no share in the formation of the 
anterior pyramids *. The central grey substance, on each side of the median line, with 
the corresponding cornu, are now represented by H tV o e (compare figs. 1, 2, 8, 4 & 5). 
In fig. 6, which represents a transverse section a little higher up, just below the bulb of 
the posterior pyramids, we see that the anterior part (f) of the central grey substance 
immediately surrounding the canal, is distinct from the posterior part (t), which covers 
it as by a kind of slanting roof. This latter is the vesicular tract or nucleus which 
gives origin to the upper roots of the spinal-accessory nerves. The anterior part (f) is 
the vesicular tract or nucleus of the hypoglossal nerve, and is the analogue of a portion 
of the anterior or motor cornu of the spinal cord. These cornua are now scarcely 
distinguishable, but their places are traversed by roots of the hypoglossal nerves in 
their passage outward from their nuclei. Traversed also by these roots, and lying on the 
outer and back part of each anterior pyramid (y), is a layer of small cells which, higher 
up, form the anterior or inner part of the lamina of the olivary body ( Ji , figs. 7 & 8). 
On the outer side of this layer is another distinct group of cells ( s ) connected by a network 
in the lateral column, and by nerve-fibres from the grey tubercle (e). This is the antero- 
lateral nucleus. Meanwhile the post-pyramidal and restiform nuclei ( b ', o) have increased 
in size, and from these, especially the post pyramidal, proceed the chief portion of the 
decussating fibres which sweep round the front of the canal to enter the anterior pyramids. 
(4) In ascending the medulla, the changes just described continue to increase in 
extent, and an important modification may be observed to take place. Fig. 7 repre- 
sents a transverse section on a level with the lower part of the olivary bodies. Here the 
posterior pyramid (b) is nearly filled with its grey substance (b 1 ) ; and that of the resti- 
form body (o) has also greatly increased, although it is still covered by a considerable 
layer of white substance (c), by which it is separated, on the one side, from the postpy- 
ramidal nucleus (b r ), and on the other side from the grey tubercle of Kolando (e). The 
spinal-accessory nucleus (t) and the hypoglossal nucleus (t 1 ) have become enlarged and 
somewhat modified in shape. The latter (£'), on each side and in front of the elongated 
canal, now contains the large multipolar cells which give origin to the upper roots of 
the hypoglossal nerve (x). As in fig. 6, a number of fibres proceeding from the poste- 
rior pyramids ( V ) sweep round in a direction forward and inward, and decussate in front 
of the hypoglossal nucleus ; but instead of plunging into the opposite anterior pyramid, 
as they didin fig. 5, they terminate in the opposite lateral and olivary column. Further 
outward and forward, other areiform fibres, proceeding from the grey tubercle (e), and 
* See my memoir -on the Medulla Oblongata, fig. 19, Plate XY. Philosophical Transactions, Part I. 1858. 
2 p 2 
