as indicative of the Age of the Animal. 
359 
will be noticed that, having recently displaced the temporary, 
these incisors are not yet i,ig 55 , 
on a level with the middle 
pair. A short time how- 
ever will suffice to effect 
this, and usually by the 
second year of the pig's 
age they are not only level 
with the others, but will 
give evidence in common 
with them of slight wear. 
It may here be re- 
marked that the cutting 
of either pair of the per- 
manent incisors above or 
below is occasionally de- 
layed by an abnormal 
position of the temporary 
teeth, sometimes depend- 
ing on an unequal breadth 
of the two jaws. In a 
specimen of this kind now 
before me, the putting 
up of the middle incisors 
in the upper jaw has 
driven the coiTesponding 
temporary teeth of the 
lower jaw aside, effecting 
a distance of more than 
an inch between them. 
Other causes, too, will 
alter the bearing of the 
upper and lower teeth on 
each other, and so inter- 
fere with the regularity of 
teething. 
Such circumstances 
now and then lead to a 
persistency of one or more 
of the incisors, giving the 
animal art' increased num- 
ber of these teeth, as has 
been shown to be the case 
occasionally in the ox, 
* Fig. 55. Lower jaw of an 1 8-months-old pig, showing that dentition is com- 
pleted ; all the teeth being now permanent. 
