614 
MR. J. L. CLARKE’S RESEARCHES INTO 
by Foville* as the grey commissure of the chord; and by Stilling'!' as a circular 
commissure composed of exceedingly delicate grey nerve-fibres. To me, however, 
its structure appears to consist of a circular layer of extremely fine fibrous tissue 
(for supporting the sides of the canal), left unobscured by the transverse commissural 
fibres which arch round it in front and behind. Indeed, it may be seen, at some 
parts of the chord, to be continuous with the areolar tissue which extends from the 
borders of the anterior fissure, through the white columns, in front of the canal. It 
varies, also, in shape at different parts of the chord, being fusiform from side to side 
in the higher regions, where the curves described by the anterior and posterior 
transverse commissures are least; and nearly circular in the lower regions, where 
those curves are greatest. The walls of the spinal canal are lined with a layer of 
columnar epithelium, which in a transverse section of the chord, viewed by direct 
light, appears as a white opake ring at the margin of the foramen 
Of the Nerve-vesicles of the Spinal Chord. 
The vesicles found in the grey substance of the spinal chord are either circular, 
oval, pyriform, or otherwise irregular in shape; and all of them, except those peculiar 
to the substantia gelatinosa, have remarkably delicate processes issuing from their 
sides, like the neck from a flask or funnel (see Plate XXV. fig. 15). They are found 
chiefly in the anterior cornua and in i\\e. posterior vesicular columns^. They are also 
connected with each other by their processes, which divide and subdivide into smaller 
branches, so that the space between them appears to be occupied by a minute network 
of the most delicate fibrils ||. Many of these processes, particularly from vesicles 
situated near the border of the grey substance, run out into the white columns, 
through fissures which contain blood-vessels and pia mater. Whether they give oflF 
branches which follow the vascular network through the white columns, I have not 
been able to determine. That the caudate vesicles have some important relation to 
the functions of the nerves, there is every reason to believe, since we find that they 
not only invariably exist in the vicinity of nerves, but, as already shown, that they 
increase also in number in direct proportion to the size of the nerves with ivhich they 
are associated. I am aware that several continental physiologists of eminence assert 
I 
Traite Complet de I’Anatomie, &c. du Systeme nerveux Cerebro-spinal. 
t Textur des Riickenmaiks, p. 23. 
I It was suggested to me by Mr. Bowman, of King’s College, that as the spinal canal is continuous with 
the fourth ventricle, it is probably lined with epithelium, which, on careful examination, I found to be the case. 
§ The situation and connections of these two longitudinal columns of vesicular substance render them ex- 
tremely interesting. They would seem to have some intimate relation to the functions of the posterior roots 
of the nerves, many of which, as already stated, traverse and surround them, without, however, forming with 
their vesicles any apparent connection. At the upper part of the medulla oblongata they are reduced in size 
and ultimately disappear. The processes radiate from their vesicles on every side ; some extending to the ex- 
tremities of the posterior cornua, and others into the lateral and posterior white columns. 
II A somewhat similar description is given by Todd and Bowman, Physiological Anatomy, p. 214. 
