306 
On the Teeth of the Ox, Sheejy, and Pig, 
In concluding this portion of my subject, I will merely observe 
— 1st, Tliat, for reasons adduced in a note, it appears to me 
that the Dentine is formed beneath the original membranous 
covering of the papilla ; 2ndly, That this membrane is the true 
same parts in fig. 9 of the diagram, which represents the young tooth as cutting 
through its sac and the gum. 
Having now shown that the membrane remains as a covering to the papilla, its ' 
office has next to be inquired into. This is, I believe, to form the enamel, for it 
appears to me tliat the ho-called performative membrane of the dentine is identical 
with the mlarri'diliue membrane of the enamel; that, in fact, there are not two 
membranes, but only one. 
The general received opinion seems to be that the outer pulp produces the 
enamel, and the inucr surface of the sac, that is, the tooth capsule, tlie crusta 
which lies both upon the faugs of the tooth and also upon the surface of the enamel, 
where it covers the dentine. This opinion is negatived, however, by the fact that 
the capsule is not reflected into the enamel cups of compound tcel/i, although these are 
always filled with crusta, and therefore it is evident that this crusta has some 
other source, and this I am inclined to believe is the outer pulp. If this pulp 
produces the crusta in one part, it necessarily would do so in another. If within 
the enamel cups, then on the outer surface of the enamel, and also on the fangs of 
the teeth. Further confirmation of tliis opinion will be presently given. 
Although tlie formation of tlie crusta succeeds that of the enamel, the two are 
so intimately bound together that it is with difficulty their developments can be 
separately described, and especially in a popular account, where one has to abstain 
as much as possible from an undue employment of scientific terms. 
First, of the enamel membrane, as I propose to call the original covering of the 
papilla in its now altered condition. If a permanent molar tooth of a lamb,, 
sufficiently developed to have a thin layer of euamel on its body, be removed from 
the jaw with its capsule entire and dissected under water, a membrane, wliich is 
interposed lietween the outer pulp and tlie forming enamel, can be readily floated 
from the surface of the latter. This, the enamel membrane, firmly adheres to the 
tooth at that part from which the fangs arise — in short, as far down as the enamel 
extends. The fonninj fnmjs are rnated v ith the outer j)'dj>, whicli nowhere else, 
from the interposition of the membrane, can come in contact with the dentine. 
See fig. 9 of tlie diagrauj. The pulp existing here, as the formative organ of the 
crusta, depends on the circumstance that the capsule is continued, independent of 
the enamel membrane, to the end of the develoj^imj fang, by adhering firmly to the 
lowermost part of the papilla. 
Todd and Bowman, in describing the development of a simple tooth, state that 
which is perfectly correct, namely, " tliat the reflection of the original mucous 
membrane of the follicle on to the papilla takes place at a line corresponding 
nearly to the neck of the future tooth, and tliat the original papilla answers to the 
crown or body of the tooth, and not to the root. The latter is a subsequent 
formation, and is laid down gradnallj' after a certain amount of ossification has 
already taken place in the crown, and after the enamel has been calcified." — 
Fliysiological Aunlomg, part iii., p. 177. 
The enamel menibrane also, on the ujiper part of the young compound tooth, is 
reflected, after the manner of an inverted finger of a glove, into the enamel cup 
(b, figs. 13 and 14), because it is not divided, as before explained, in the 
cleavage of the papilla, to produce this variety of tooth. The inverted portion of 
the membrane has between its folds some of the outer pulp, and thus the crusta is 
ultimately produced within the cup. 
Examined under a low magnifying power the surface of this membrane, which 
is in contact with the newly deposited enamel, and which has undergone a change 
equal with its outer or original epithelial surface, seems to be merely linear in its 
arrangement ; but when magnified 2(K1 diameters, columns or elongated prismatic 
cells of forming enamel are readily detected upon it. In the annexed engraving 
these prismatic cells (a, fig. 15) are represented in situ as they would be seen in a 
vertical section of the pulp, n, shows the enamel membrane by which they are 
