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On the Teeth of the Ox, Sheep, and Pig, 
The varying sizes of these rings, and the sudden cui'vatures of 
the dentinal tubes in these places, would seem to indicate an 
irregularity in the rate of formation. 
In a tooth with more than one fang, as for example the molar 
of a pig, when the sides of the pulp are covered with dentine, 
a horizontal projection of this substance shoots across the base of 
the pulp. By this means one fang becomes separated from the 
other, and the same process of conversion goes on in each lower 
division of tlie pulp until the final length of the fangs is accom- 
plished. Tliis circumstance explains how it is that in a molar tooth, 
in particular, a section, made in a vertical direction through its 
middle, exposes a cavity of a similar shape to the tooth itself. 
The irregularities on the face of a tooth forming its points 
or cusps are simply caused by the papilla assuming that form, 
before any dentine is produced upon its surface. This brings me 
to the f^uestion of the formation of compound teeth, as in them 
we find deep depressions in the dentine into which the enamel 
dips. These depressions are effected by a kind of cleavage of the 
upper part of the papilla or tooth pulp to a depth corresponding 
with that of the hollow. Thus, supposing a tooth to have two 
principal cusps with an enamel cup between them, the substance 
of the papilla recedes from the centre and forms two apices. 
Each of these becomes first capped with a layer of dentine, as 
seen in the subjoined engraving, fig. 13, and next covered with a 
Fig. 13.* Fig. 14.f 
layer of enamel. The "enamel membrane," hereafter to be more 
particularly described, is present in these hollows, because in the 
* Fig. 13. Vertical section of a molar tootli of a young calf while being 
developed, showing tlie formation of the enamel cup. a, the pulp cavity ; B, the 
enamel cup still open at the bottom ; », the dentine ; e, the enamel. 
t Fig. 14 also represents a vertical section of a similar tooth, and shows that the 
enamel cup is now closed at the bottom by a further production of dentine, a, the 
pulp cavity ; b, the enamel cup ; d, the dentine ; and e, the enamel. 
