276 ME. J. L. CLAEKE ON THE INTIMATE STEUCTUEE OF THE BEAIN. 
VIII. these arciform fibres are seen between n and N. They pass between the separated 
longitudinal bundles n'" of fig. 27, Plate X., where their cut ends are represented by the 
dark dots, and between other transverse fibres proceeding outwards from the spinal- 
accessory nucleus ; and this kind of plexus through which they pass contains numerous 
nerve-cells whose processes are continuous with the different sets of fibres. 
The next or internal layer (t t ) of fig. 27, Plate X. is the spinal-accessory nucleus 
or tract, the cells having been omitted to avoid obscuring the fibres. It has been already 
stated that a multitude of these fibres run longitudinally. In fig. 25, Plate X. it has 
been shown that a vast number run transversely outward, from G to the slender column 
n and to the lateral column beyond it. In the oblique longitudinal section (fig. 27) we 
see both sets of fibres together. The longitudinal are not quite parallel, but intersect 
each other at different angles, and bend round to be continuous with the transverse. 
The latter then run outward, between the other set of transverse arciform bundles (n", 
fig. 27, dark dots) (and n, fig. 5, Plate VIII.), which cross them at right angles as they 
sweep round from behind forward to the anterior pyramid. On reaching the slender 
column (n, fig. 27, Plate X.) some of them run with it longitudinally; but by far the 
greater number, frequently in bundles, continue their course outward, and cross it more 
or less at right angles to enter the layer n 1 n'", where they contribute to form the grey 
network between the longitudinal and the outer transverse arciform bundles. With the 
former of these bundles ( n fig. 27, Plate X.) some of them are directly continuous; 
and with the latter (represented by the dots at n "') others appear to be connected through 
the medium of the intervening cells : the rest continue outward across the fine longitu- 
dinal fibres of the next layer, d', where similar connexions with the cells and longitudinal 
fibres appear to take place ; some of them reaching the superficial white column d, in 
which they become lost. 
The course and arrangement of the different sets of fibres in this extremely compli- 
cated structure may now perhaps be more completely understood, if we suppose the lon- 
gitudinal section (fig. 27) to be applied with its plane perpendicular to the planes of the 
transverse sections (fig. 8 & fig. 5, Plate VIII.), so that the upper border (t) of fig. 27 shall 
coincide with the line L t of fig. 8, and its lower border (L t) with the same line in fig. 5. 
In descending the medulla below fig. 5, Plate VIII., the innermost fibres (n 1 ) of the 
layer d' (fig. 27, Plate X.), in which the slender column n terminates, become still 
further removed from the central nucleus (t) of the spinal-accessory nerve, by the inter- 
position of lateral grey substance, with which the lower roots of this nerve are connected, 
the cells of the central nucleus behind the canal being now small and sparing in number. 
Fig. 28, Plate X. represents the left lateral half of the grey substance of the medulla 
between figs. 4 & 5, Plate VIII. The central nuclei of the spinal-accessory and hypo- 
glossal nerves (t, t') are only just marked out around the canal, while the lateral grey 
substance beyond them is crossed by portions of the remaining curved bundles proceeding 
from the restiform and postpyramidal nuclei to the decussation of the pyramids, which 
have ceased to derive their fibres from the lateral columns, that part of those columns 
