THE STRUCTURE OF THE SPINAL CHORD. 
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that they have discovered in the lower vertebrata and in the invertebrata a direct 
union between the caudate vesicles and the tubular fibres ; but I have never been able 
to make out satisfactorily any such connection in the. spinal cliord of mammalia, 
although I have constantly sought for it under very favourable circumstances*. The 
nerve-fibrils wind around, and apparently in contact with, the vesicles, but the con- 
nection does not seem to have at all the character of an attachment. Nor have I 
succeeded in tracing anything like continuity between the tubular fibres and the 
processes of the vesicles. It is very common to see one or two of these processes 
running outwards into a bundle of nerves attached either to the anterior or poste- 
rior cornua ; but then we have seen that they pass out into the white columns from 
all sides, and therefore from parts which are not connected with nerves. 
Blood-vessels of the Spinal Chord. — These enter through the anterior and posterior 
median fissures, through the smaller fissures in the white columns, and at the roots 
of the nerves. After giving off numerous branches to the white columns, they pro- 
ceed inwards to the grey substance, along the whole periphery of which they form a 
remarkably beautiful network of loops'!-, intermixed with nerve-tubes and some of 
the processes of the vesicles. Within the grey substance they form an extremely 
minute network. Some of the vessels which enter at the anterior and posterior fis- 
sures and at the posterior white columns, anastomose with each other around the 
spinal canal ; while others branch off, right and left, between the bundles of the 
transverse commissure, into the anterior and posterior cornua, where they follow the 
course of the transverse fibres, and running to the peripliery of the grey substance, 
assist in forming there the loops already described. A series of loops is also found 
to exist near the extremity of the posterior cornua, along the border of the spongy 
substance. 
Of the White Columns of the Spinal Chord. 
The anterior white columns of the chord have no proper transverse commissure, 
but are united in the middle line, at the bottom of the fissure, by a fibrous band or 
raphe. In this situation, however, they are crossed transversely by horizontal and 
oblique tubular nerve-fibres and blood vessels proceeding from the grey substance 
on either side, and which, in some regions of the chord, are so numerous that they 
nearly replace the longitudinal fibres:|:. The transverse slits observed by Foville on 
each side of the raphe are fissures for the passage of blood-vessels. 
* Hanover is, I believe, the only observer that professes to have seen it in all classes of vertebrata. 
f According to Dr. Stilling this network consists of the (sO'Called) grey transverse fibres. He confesses, 
however, that it is not unlike a network formed of small blood-vessels. — Textur des Riickenmarks, p. 22. 
1 Stilling maintains that the separation of the anterior white columns is complete, for at the bottom of the 
fissure may be seen “ the transverse grey fibres of the anterior commissure.” — Ueber die Medul. Oblong, p. 6. 
The fibres, however, which give to this structure its grey or yellowish-grey appearance, are really blood-vessels 
and pia mater. 
4 K 2 
