612 
MR. J. L. CLARKE’S RESEARCHES INTO 
posterior cornua, some of their vesicles reaching as high as the substantia gelatinosa. 
As a further result of the same changes, the posterior white columns are much deeper 
and broader here than in the lower regions of the chord (compare Plates XX. and 
XXL figs. 3, 4, 5 and 6). 
While the posterior masses of the grey substance are undergoing the modifications 
just described, a series of somewhat similar alterations are found to take place in the 
form and arrangement of the anterior masses. In the middle of the lunibar enlarge- 
ment, the anterior cornua have increased to a still greater extent than the posterior, 
and have assumed a shape the opposite of that which they possessed lower down in 
the chord. They now turn rather outwards instead of inwards, and have a large, 
irregularly club-shaped, instead of a pointed, extremity. The caudate vesicles have 
become exceedingly numerous, and are grouped together in several large masses, 
which are situated chiefly on the outer and middle parts of the cornua (fig. 6). They 
lie in the meshes of a net-work formed by bundles of fibres proceeding from the 
anterior and posterior roots of the nerves, and from the commissural bands behind 
the spinal canal*. 
On proceeding upwards from the lumbar enlargement into the dorsal region of the 
chord, arrangements in the grey substance are observed to take place in the reverse 
order of those already described. By degrees the posterior cornua are reduced in 
length, and somewhat modified in shape ; their inner sides extend towards each other 
and the middle line, while the posterior bands of the transverse commissure are 
drawn, as it were, gradually backwards, becoming at the same time less curved ; so 
that the space between them and the spinal canal is now correspondingly increased. 
Into this space the two posterior vesicular columns advance between the fibres of the 
transverse commissure, together with the inner sides of the posterior cornua, which, 
in the middle of the dorsal region, coalesce and inclose them behind. (Compare 
Plates XXII. and XXIII. figs. 7? 8, 9 and 10.). Here, then, the posterior grey sub- 
stance again consists only of a single mass, and again, also, the substantia gelatinosa 
extends uninterruptedly and nearly horizontally across from side to side. On the other 
hand, the anterior cornua are long, straight and narrow, and project almost directly 
forwards. The caudate vesicles, reduced considerably in number, are scattered irre- 
gularly through them, but are more numerous towards their extremities, where they 
are sometimes seen in the form of one or two small groups. 
From the middle of the dorsal region to the cervical enlargement of the chord, the 
alterations in the form of the grey substance are once more reversed, being nearly 
similar to those which are found to take place on proceeding upwards from its lower 
extremity. The posterior mass renews the process of division into two parts, com- 
mencing with the substantia gelatinosa at the middle line, where the transverse com- 
* It is interesting, in a physiological point of view, to find that the number of caudate vesicles is in direct 
proportion to the size of the nerves, which are known to be much larger at the lumbar and cervical enlarge- 
ments than in other regions. 
