MB. J. L. CLAEKE OX THE OBEY SUBSTAXCE OF THE SPINAL COED. 445 
Around the whole of the cylinder, and partly encroaching on its border, other cells 
are disposed, that contribute to form, by their collective processes, an irregular circle of 
hbres; but these individually^ after describing parts of the circle, run off tangentially 
in different directions (fig. 2, Plate XX.). On the outer side of the cylinder they cross 
each other obliquely from before backwards and vice versa, extending in opposite 
directions to the anterior and posterior cornua. They also contribute with the posterior 
roots to form the transverse commissure behind the central canal. The cells are of all 
sizes, and mostly fusiform—often to a remarkable degree ; but some are triangular and 
stellate. Many are curved and elongated circumferentially ; others are inclined at a 
tangent, and send off their processes, on the one hand, within or around the circle, and, 
on the other, to distant parts. Sometimes an irregular or stellate cell sends two of 
its processes round the circle, one longitudinally or obliquely, and the rest in other 
directions, but mostly towards the anterior parts, or towards the lateral column. 
When the posterior roots of the nerves are traced inwards, they are found to be most 
intimately connected with all parts of ih.e ])Osterior vesicular columns. One large bundle 
is generally observed proceeding from near the middle of the caput cornu to the outer 
side of the cylinder, where its fibres diverge or separate : some of them partly enclose it, 
apparently in connexion ^^nth the cell-processes ; Avhile the rest interlace within it, or 
form a series of tortuous curves, as may be seen best in a longitudinal section ; or after 
running longitudinally backwards and forwards, in a kind of looped or zigzag course, 
escape into the lateral white column*. Another large bundle (P) invariably enters 
along the inner side of the caput comu near the posterior median fissure ; some of its 
fibres return backwards towards the point and outer side of the gelatinous substance, 
partly to form loops with other roots, and partly to escape through the lateral white 
columns ; some interlace through the cylinder ; some sweep round on its outer side and 
join both the posterior and anterior commissure, while others are prolonged forwards 
through the lateral portion of the cendx cornu. 
A band of fibres from the posterior transverse commissure, after curving round the 
front of the vesicular cylinder, runs nearly horizontally outwards (as seen in a transverse 
section) to the lateral border of the grey substance and lateral column (see figs. 2, 
o & 4). These fibres, which are more conspicuous at the upper and lower parts of the 
dorsal region, are joined by others, which proceed from the inner side of the cylinder, and 
horn a different 'plane \ for at this point they are cut across in the section, and terminate 
abruptly in divided extremities f. The lateral portion of the grey substance which is 
It is difficult, however, to determine whether these tortuous and zigzag fibres are directly continiious 
with the posterior roots, or with the processes of the cells, for their diameters are often considerable. 
t This appearance is observable chiefly in the upper and lower parts of the dorsal region, but particularly 
the latter ; it is also to be seen in some degree in the cervical and lumbar enlargements ; in the upper part 
of the latter it is very conspicuous. At the point where these fibres are divided in the transverse section, 
that is, at the inner side of the posterior vesicular column, and a little behind the spinal canal, they appear 
to be continuous vith the tortuous and zigzag fibres seen in a longitudinal section, as above described. 
MDCCCLIX. Q 
O X\ 
