610 
MR. J. L. CLARKE’S RESEARCHES INTO 
fissure, some of these fibres cross obliquely through the anterior white columns, and 
decussate with corresponding fibres from the opposite side (see Plate XX. figs. 1, 3, &c.). 
Latero-transverse Fibres. — The second order of transverse fibres take a more or less 
horizontal direction between the opposite sides of the grey substance, forming the 
transverse commissure, and are arranged chiefly in loose bundles (see figs. 2 and 3). 
Those behind the spinal canal diverge on each side into the anterior and posterior 
grey masses, and extend into both the posterior and lateral white columns ; a great 
number being evidently continuous with both the anterior and posterior roots of the 
nerves. One large bundle, in the centre, is particularly conspicuous (see figs. 2 and 3). 
Those in front of the spinal canal are much less numerous and curve principally for- 
wards : they may be traced partly into the antero-lateral columns, and partly into 
the anterior roots of the nerves. 
By Dr. Stilling some of the fibres of the posterior nerves are said to cross over, 
behind the spinal canal, into the anterior cornua of the opposite side. I have many 
times thought that such an arrangement really exists, but the inquiry is attended 
with great difficulty, and my own observations, though frequently repeated, are too 
uncertain in their results to admit of my confirming or denying the existence of 
these fibres. Hanover denies that there is any crossing of the fibres in the spinal 
chord. He says, “ Une partie des fibres passe bien d’un cote de la moHle epiniere a 
I’autre, mais im entre-croisement general n’a pas lieu*.” 
Longitudinal Fibres. — The fibres of the substantia gelatinosa are, as usually de- 
scribed, chiefly longitudinal. When examined immediately after death, and uninjured 
by pressure or traction, they have all the characters and appearance of minute tubular 
fibres, presenting dark, single, and sharply-defined outlines, with frequent varicosities ; 
but when stretched, or otherwise injured by manipulation, they lose their dark 
borders, and become exceedingly pale and delicate^- They vary but little in size, 
but are all extremely slender, their average diameter not exceeding the i^th of an 
inch : some few are larger, but I have seen numbers as small as the or i^olh of 
an inch in diameter, as shown by the micrometer. They are usually distinguished 
as grey fibres, but differ in many respects from the grey fibres contained in the sym- 
pathetic system of nerves ; for they are not only, on an average, finer, but, like the 
tubular fibres, are little or not at all affected by acetic acid, which fails to bring out 
any traces of nuclei They have also been said to resemble the processes of the 
his own words “ Die Primitivfasern der Nervenwurzeln nichts Anderes sind als die unmittelbaren Fortsatze der 
queerlanfenden grauen Substanz des Riickenmarks” (Textur des Riickenmarks, p. 28). The transverse fibres, 
however, are really white tubules of smaller diameter than those which form the roots of the nerves. 
* Recherches Microscopiques sur le Systeme Nerveux, p. 14. 
t The method adopted for examining these fibres was as follows ; — a thin longitudinal section through the 
substantia gelatinosa was made by a rapid stroke with a very sharp instrument, w'et with albumen. The sub- 
stantia gelatinosa was then carefully separated from the parts on either side of it, and examined without any 
pressure beyond that produced by the weight of the thin glass employed to cover it. 
I Remak states that they are nucleated. Drs. Stilling and Wallace describe them as grey nerve-tubes 
