312 
Oil the Tcetli of the Ox, Sheep, and Pig, 
the development of tlie permanent, which are to replace them, 
as well as for those molars which, in due time, are put up and 
add to their number. 
The order in which the two sets succeed each other, together 
Avith the cutting of the additional permanent molar teeth, consti- 
Fig. 20.« 
tutes dentition. To tliese phenomena, as they occur in the ox, 
sheep, and pig, I have now to direct the reader's atterition, as a 
means by whicli we can determine the age of these animals. Their 
value for such a purpose will become apparent as we proceed. 
This may be called the more practical part of my subject. As 
such it will necessarily require fidl investigation, and I shall 
direct attention, firstly, to the Dentition of the Ox. 
DENTITION OF THE OX. 
The causes of the fall of the temporary teeth, and the way in 
which that is effected, will at the outset require our notice. 
Three principal causes are in operation together to produce the 
fall of the temporary incisors ; these are, wear, greater width 
of the animal's jaw from increasing years, and the pressure of 
the advancing teeth ; to these some minor things might be 
added. 
That the fall of the temporary teeth, as a general principle, 
depends more upon the rate of the development of the permanent 
beneath them than upon either their own wear or the spread of 
the animal's jaw, seems however to be evident. As the perma- 
nent teeth grov/, so do they press upon the fangs of the temporary, 
* Fig. 20. Transverse section of the upper part of a permanent molar of 
a sheep magnified with a lens only to show the arrangement of its several 
constituents, u, the pulp cavity slightly open ; c, the crusta ; v, dentine ; e, 
enamel. 
