2(34 
ME. J. L. CLAEKE ON THE INTIMATE STEUCTUEE OF THE BEAIN. 
section is begun, the hardened medulla should be macerated for a few days in strong 
spirit to which a small quantity of liquor potassse has been added. 
(2) At the highest point of the spinal cord, that is, at the first pair of cervical nerves, 
a transverse section of both the white and grey substances has the appearance repre- 
sented in fig. 1, Plate VIII. Here the central grey substance ( t ) surrounding the canal, 
is of considerable size and of somewhat quadrangular shape. The neck of the posterior 
horn, cervix cornu posterioris , between V and o, is very slender, and after stretching 
obliquely outward and backward from the middle line, terminates in a tuft or expanded 
extremity (V), which I have named the head or caput cornu posterioris. Between the 
central canal and the bottom of the anterior median fissure ( z ) are seen the decussating 
fibres of the anterior commissure extending on each side into the anterior white column ; 
and in the deep and somewhat oval space (d!) of the lateral column (d) is a beautiful 
network of nerve-fibres and blood-vessels extending from the borders of the surrounding 
grey substance, and enclosing in its meshes a number of separate fasciculi which, a 
little higher up, in the medulla oblongata, cross over to the opposite side in front of the 
canal, and with the corresponding fibres of the anterior commissure, form the opposite 
anterior pyramids (see fig. 2). This network in the lateral columns contains a number 
of cells of different shapes and sizes, and which in animals are larger and more nume- 
rous than in Man. 
(3) At the lower part of the medulla oblongata, that is, at the points of the anterior 
pyramids, a transverse section presents the appearances delineated in fig. 2. Here the 
central grey substance (t) has become narrower laterally, but has increased a little in depth 
from before backward in the middle line, and the posterior cornua (b', o, e) are some- 
what depressed or thrown more to the side of the medulla. The head or caput cornu 
posterioris ( e ) has increased in size, and begun to detach itself from the extremity of the 
cervix (o), being joined to it only by a small network containing slender bundles of lon- 
gitudinal fibres, while the cervix itself has become a little thicker and more bulbous. 
Meanwhile, the bundles of longitudinal fibres contained in the meshes of the lateral 
^columns cross over to the opposite side and plunge into the anterior columns to form 
the anterior pyramids at z. Ascending a little higher in the medulla (fig. 3), we find 
that while the caput cornu posterioris continues gradually to enlarge, it becomes more 
and more detached from the extremity of the cervix, or rather, is joined to it only by an 
increase of the intervening network already mentioned. At the same time the central 
grey substance ( t ) is encroached upon at the sides of the canal by the bundles of the 
lateral columns destined for the anterior pyramids ; so that it has now a triangular shape, 
and together with the posterior cornua has some resemblance to a bird with both its 
wings expanded. From the root ( V ) of the posterior cornu, on each side of the poste- 
rior median fissure, there now arises a grey network of fibres and blood-vessels con- 
taining nerve-cells and extending backwards through the posterior pyramid (b) to form 
the rudiment of its grey nucleus, or the post-pyramidal ganglion. Still further out, or 
nearer its extremity, the surface of the cervix cornu is raised into an eminence (o) which 
