756 
MR, A. SANDERS ON THE ANATOMY OF THE 
or less resembling the granular or molecular layers are found in other parts, but 
Puekinje cells occur nowhere else. In Scyllium the granular layer does not extend 
so far back as the molecular. The same may be said of Rhina and Acantbias. 
Spinal Cord. 
The grey matter of the spinal cord (figs. G, 7, and 8) has somewhat the shape of a 
goblet with its foot. The dorsal horns spread out towards the dorsal surface in a 
way to make it resemble a Lucernaria ; this resemblance is more apparent in Acanthias 
than in the figure. The ventral horns are extremely well defined and distinct, they 
extend horizontally on each side of the central canal, in shape like a pair of clubs. 
Surrounding the central canal there is a single-celled layer of endothelium to be 
observed; and external to that a space of connective tissue which may be compared 
to the substantia gelatinosa centralis. In a transverse section one may reckon four 
columns of longitudinal fibres. Those beneath the ventral horns of grey substance 
may be termed the ventral columns, situated between the central canal and the 
ventral surface of the cord, and bounded on each side by the ventral roots of the 
spinal nerves. The lateral columns extend from the outer sides of the ventral roots 
to the external side of the dorsal horns. The remaining trvo columns are the dorsal 
situated above the dorsal cornu, and a small pair of fasciculi placed immediately dorsad 
of the central canal above the connecting link between the tw T o ventral cornua. In 
addition to these there are a few small bundles running longitudinally through the 
dorsal cornua, which are the dorsal roots of the spinal nerves. The ultimate destina¬ 
tion of these columns will be seen presently, as far as 1 have been able to unravel 
their course. Each ventral horn of grey substance contains about nineteen or twenty 
cells in one section. These cells are of a larger size than those found in the ventral 
horns in the Teleostei; they are generally elongated, and give off several processes ; 
they are arranged in an imbricated manner, with their long axes diiected obliquely 
from the ventral to the dorsal surface. As the spinal cord passes on to merge into 
the medulla oblongata, the ventral cornu becomes depressed towards the ventral edge 
of the cord, so that instead of being placed in a horizontal position, it gradually 
comes to form an angle of about forty-five degrees. Immediately behind the posterior 
end of the fourth ventricle it begins to disappear, but some of the cells may be traced 
in the corresponding position for a few sections farther forward, and they finally 
disappear at the posterior end of the medulla oblongata. At this point another 
ganglion becomes apparent, which is not a continuation forward of the ventral cornu, 
but is situated nearer the central line and the dorsal surface in the grey matter of the 
floor of the fourth ventricle, rather to its outer side. It forms part of the origin of 
the vagus. The fibres of the ventral column vary in size, but they are larger than 
those of the lateral and dorsal columns ; their average diameter is less than that of 
the corresponding fibres in the spinal cord of the Teleostei. 
