-HENDRY, ON THE NERVE-CELLS IN THE OX. 41 
this median armature is wanting in the “ spoon,’ whose 
edges also in that species are armed, not with sharp denti- 
cles as in all other instances I have as yet seen, but with 
blunter transverse ridges—presenting, in fact, pretty nearly 
the same difference that exists between the dentition of 
Mustelus levis, and that of other dog-fish. The only other 
essential point to which I need refer, is the serration or den- 
tition, as it might well be termed, on the edges of the valve. 
This armature usually consists of a series of very fine teeth, 
extending from the hinder end of the border throughout its 
whole length, except at the point where it may be interrupted, 
as appears usually to be the case, by one or more considerably 
larger denticles on each side, or at the apex. Besides this, the 
margin may be either straight, as in Amphidotus and Echinus 
sphera and the “jaw,” or scalloped as in Kchinus lividus. 
And doubtless numerous other variations will be met with. 
Now, upon inspection of the figures, it will be seen that all 
these parts, except the hinder door-knocker process, which is 
wanting in every specimen, being easily detached from the rest 
of the valve, are exhibited in the “jaw.” The letters in each 
figure are applied to the corresponding parts. 
a. The serrated margin. 
4. The larger denticles. 
ec. The median ridge or kelson, with a large denticle in front. 
d. The lateral condyles. 
On the Nerve-Ce ts of the Spinau Corp in the Ox. 
By W. Henpry, Surgeon (Hull). 
Tue careful and patient manipulation required in order to 
display and mount the nerve-cedis of the cord has undoubtedly 
tended to retard any general knowledge of these most singular 
and interesting bodies, whose structure and relations have 
hitherto remained in comparative obscurity. They are nume- 
rous and well-defined corpuscles, exeeedingly variable in size 
and form, and furnished with conspicuous circular nuclei and 
nucleoli, of a yellowish colour, and usually presenting towards 
one or other extremity a pigmentary matter of a peculiar 
kind. They are also furnished with one or more processes, 
