274 
MR. J. L. CLARKE ON THE INTIMATE STRUCTURE OE THE BRAIN. 
outward, partly into the lateral column (at n), accompanied by others from the masses B, 
but chiefly into the group of cells (H) forming the anterior portion of the nucleus, and 
are interspersed not only with small cells, but with numerous others of a larger kind, 
which are oval or fusiform, and elongated in the same oblique direction. They decussate 
with those in the opposite half of the nucleus across the central line at G. Many of 
them are evidently derived from a mass of epithelial cells situated at E between the 
bases of the posterior pyramids. 
The anterior portion of the spinal-accessory nucleus consists of an oval or fusiform 
group of cells (H), sloping forward and outward from behind the canal. The cells are 
of various sizes, are mostly oval, and lie with their longer axes in both a transverse and 
longitudinal direction. Many of them are filled with dark pigment. From the outer 
and anterior extremity of this group fibres proceed to form the greater part of the 
spinal-accessory nerve r ; and from its inner and posterior extremity another set of fibres 
extend obliquely inward and backward behind the canal, to the opposite group of cells. 
These commissural fibres, like the others that decussate between the opposite sides of 
the spinal-accessory nucleus, are not so distinct in Man as in the Ox, Sheep, Cat, Dog, 
or Rabbit, and are most conspicuous at a lower level of the medulla, especially at the 
inferior extremity of the olivary bodies, in sections corresponding to fig. 6, Plate VIII. 
Between this group of cells in the anterior portion of the nucleus, and the curved 
outer fibres (A A) proceeding from the posterior portion, is a roundish or somewhat oval 
column of longitudinal bundles ( n ), either wholly or only partially enclosed on its pos- 
terior and inner sides by a band of fibres (M), which sweep forward and inward across 
the root of the spinal-accessory nerve r, and round the hypoglossal nucleus (J) to the 
median raphe (F), where they decussate with their fellows from the opposite half of 
the medulla. This little column is at intervals interspersed with small nucleated cells, 
sometimes united by a kind of network, and is, as I shall presently show, a structure of 
great importance. 
I have already shown that at the lower end of the medulla oblongata, a network of 
fibres and cells is formed in the deep portion of the lateral column (d 1 , fig. 1, Plate VIII.) 
between the anterior and posterior horns ; that from the meshes of this network proceed 
the bundles that form the chief proportion of the opposite anterior pyramid (figs. 2, 3, 
& 4) ; and that after these bundles have ceased to cross over, the original network reap- 
pears in a finer form (fig. 5, Plate VIII.) with an increase in the size and number of its 
cells, and containing in its meshes a multitude of bundles composed of finer fibres. 
Now the deepest or most internal and posterior of these longitudinal fibres (those lying 
immediately in front of the caput cornu or grey tubercle ( e ), at the angle formed by the 
lines L n, fig. 5, Plate VIII.) diverge from the rest as they ascend the medulla, and 
curving inward and backward, form the slender column n of fig. 8, Plate VIII. and fig. 
25, Plate X. The derivation and course of this little column are well seen in a longi- 
tudinal section carefully made in a particular plane, that is, obliquely from behind 
forward in the direction of the line Lf, fig. 8, Plate VIII., or almost in the course of 
