618 
MR. J. L. CLARKE’S RESEARCHES INTO 
Of the Nerve-tubes of the Spinal Chord. 
The nerve-tube is endowed with considerable elasticity, and may be drawn out and 
attenuated to a great extent. It then loses its thick and sharply-defined borders, or 
double outline, and assumes the appearance of a much finer and more delicate fibre. 
When partially broken by traction, the two extremities are connected often by one of 
its borders only, and sometimes only by the axis cylinder, which has then the appear- 
ance of an almost imperceptible, shadowy line ; in the unbroken portion of the fibre, 
however, the axis cylinder appears perfectly pellucid. 
The following summary of the principal facts described in this paper may perhaps 
he found useful. 
That the posterior grey substance, at the lower extremity, and in the dorsal region, 
of the spinal chord, consists only of a single mass ; and that the substatitia gelatinosa 
there extends uninterruptedly across from one side to the other. 
That the nerve-fibres of the grey substance, including those of the substantia gela- 
tinosa, are not grey fibres bearing nuclei, like those of the sympathetic, but fine 
tubules. 
That two considerable columns of caudate vesicles (which I have named the pos- 
terior vesicular columns) in intimate connection with the posterior roots of the nerves, 
extend through the whole length of the chord ; commencing small at its lower extre- 
mity, increasing in size in the lumbar and cervical enlargements, and terminating at 
the upper part of the medulla oblongata. 
That the number of caudate vesicles, particularly in the anterior grey substance, is 
in direct proportion to the size of the nerves. 
That the column of vesicles into which, in the cervical region, the spinal-accessory 
nerve may be traced, extends down the chord as far as the lumbar enlargement. 
That a considerable branch of the spinal-accessory nerve, after entering the grey 
substance through the lateral column, may be easily traced to the caudate vesicles of 
the anterior cornu. 
That the spinal accessory is the only nerve immediately attached to the lateral 
column. 
That the posterior roots of the spinal nerves are immediately attached to the pos- 
terior white columns only ; and the anterior roots to the anterior columns only ; but. 
That fibres from both these roots, after traversing certain portions of the grey sub- 
stance, pass out again into the white columns. 
That neither the anterior nor posterior white columns are connected by a trans- 
verse commissure. 
That the central portion of the grey substance immediately surrounding the spinal 
canal is not a commissural structure, but a layer of fine fibrous tissue for supporting 
the walls of the canal, which is lined with a layer of columnar epithelium. 
