THE STRUCTURE OF THE SPINAL CHORD. 
613 
tnissiiral bands are gradually pressed, as it were, forwards, and thus mark out the 
posterior cornua; while in these, which again reach their greatest size in the middle 
of the cervical enlargement, the posterior vesicular columns, formerly situated behind, 
and at the sides of the spinal canal, at length resume their position and increased di- 
mensions (see fig. ] 1). During the progress of these changes, the anterior cornua also 
undergo considerable modifications. They become gradually broader and longer, 
and contain a much larger number of vesicles, which in the cervical enlargement are 
grouped together, as in the lumbar region, into several large masses; indeed, the 
general arrangements of the grey substance at these two parts of the chord have a 
very striking resemblance*. 
At the outer border of the grey substance, between the anterior and posterior 
cornua, is a small column of vesicular matter, which is softer and more transparent 
than the rest. This consists of caudate vesicles of inferior size and more regular shape 
than those usually found in the spinal chord. It is seen distinctly at the upper part of 
the lumbar enlargement (see Plates XXII. and XXIII. figs. 7 and 8 m), and increases 
somewhat in size in the dorsal region, where it projects slightly into the lateral column 
on each side. In the cervical enlargement it is less distinctly marked, but higher 
up it again becomes conspicuous, and is there seen to form the principal part of the 
nucleus of the spinal-accessory nerve (see fig. 12). On ascending the medulla ob- 
longata, this column of vesicles gradually makes its way inwards till it reaches the 
space immediately behind the spinal canal, where it meets and blends with its fellow 
of the opposite'!'. 
In the upper part of the cervical region the posterior cornua are long and narrow. 
The outer part of each, below the substantia gelatinosa, consists of a large and 
remarkably beautiful network of blood-vessels, which incloses in its meshes bundles 
of fibres of the lateral columns (see Plate XXIV. fig. 1 2). These bundles are of various 
sizes, and encroach gradually upon the cornua as they ascend to the medulla ob- 
longata. Some of the fibres of the spinal-accessory nerve run transversely through 
this network ; but a considerable branch, on entering the grey substance, bends foi'- 
wards, and after passing through its vesicular nucleus, continues the same course 
within the anterior cornu, where its fibres traverse and surround the caudate vesicles, 
in company with the roots of the anterior spinal nerves (see Plate XXV. fig. 13), The 
space behind the spinal canal has slightly increased in breadth, and the posterior 
vesicular columns on each side of it have nearly the same position and relations as in 
the dorsal region. The anterior cornua are rather small and pointed, and contain 
each a circular or oval mass of vesicles. 
The central portion of the grey substance surrounding the spinal canal is described 
* The vesicles are more abundant, however, in the lumbar than in the cervical enlargement, and therefore 
correspond in number to the relative size of the nerves which belong respectively to these regions. 
t The nucleus of the spinal-accessory nerve in the medulla oblongata has been already correctly described 
by Dr. Stilling, Die Medul. Oblong. 
MDCCCLI. 4 K 
