300 
On the Teeth of the Ox, Sheep, and Pig, 
Fig. n.* 
D-- 
tubes interspersed in its structure, and c* the Haversian system, 
which is so perfect in places as to lead to the Crusta being 
readily mistaken by a casual 
examination for true bone. 
The simplicity as well as 
the beauty of this provision 
of nature for a maintenance 
of the vitality of old teeth 
is so self-apparent that no 
necessity exists for further 
observations on the point. 
From the explanation of 
the structure of a tooth, I 
proceed to speak of the 
manner in which teeth are 
formed, confining, for ob- 
vious reasons, my remarks 
to those animals which are 
the chief subjects of these 
pages. The development of 
teeth has of late years been 
studied with much advant- 
age, and we are now enabled 
to describe the successive 
stages of the process with 
far greater confidence than 
formerly. In a work of this 
kind it is not required that 
I should enter very minutely into the subject, but merely give a 
general outline of it, so that the reader may the better under- 
stand how a second set of teeth, the permanent, spring up to 
supply the place of the temporary, after they have served their 
purpose. 
Besides the order of eruption of the teeth in two sets, which 
is the practical part of my subject, I may observe, in the lan- 
guage of Professors Quain and Sharpey, that " the develop- 
ment of the teeth includes a description of their origin and 
growth as distinct organs, and also the formation of their com- 
ponent tissues, the dentine, enamel, and cement."t The annexed 
diagram, altered from Prof. Goodsir's, will be found materially 
to assist the description ; and first, it must be observed that the 
process of formation, as a whole, has been divided into four 
w.s 
* Fig. 11. Conversion of the dentine into crusta. 
lacuna; ; c, crusta with its tubes and cells ; c*, Haversian system in crusta 
nified 200 diameters. 
t Elements of Anatomy, vol. ii., p. 981. 
D, dentinal tubes; d*, dentinal 
Mag- 
