as indicative of the Age of the Animal. 
325 
These things are more clearly marked in oxen with a comparative 
narrow jaw, such as the Dcvons. 
The general condition of the mouth at this time is shown in 
the preceding figure. It represents a front view of the lower 
jaw of an Hereford ox at one year and ten months old. 
The permanent incisors, 1, 1, are as yet not fully up, so 
that the gum is embracing rather the lower part of their 
• crowns than their necks. Although the observation will apply 
generally to all the permanent incisors, this will be a proper 
place to state that the conclusions which are arrived at with re- 
spect to age, must be always regulated by the amount of the ^ro- 
ti'usion of these teeth from the gum, as well as by their number. 
At two years oi age the last addition to the number of the 
molar teeth is made by the cutting of the sixth in situation. 
This tooth follows, as has been previously explained, the fifth 
molar, after an interval of nine months. Its being in the mouth 
at two years, although not fully developed, is a circumstance to 
be kept in mind in our investigations of age. 
The sixth permanent molar in the lower jaiv has many of the 
special characters of the third temporary molar. Its long dia- 
meter exceeds that of the fourth or fifth, but its short diameter 
is only equal to theirs at its front pai t, decreasing gradually from 
before backwards. The tooth is therefore thicker at its front than 
at its hinder part. It is also tri-lobular, like the third temporary ; 
but its lobes are scarcely so perfectly formed, or so distinct from 
each other. The hindermost one, not being of equal height with 
the others, is not unfrequently concealed by the gum long after 
the tooth is cut. Differing, however, as it does in so many par- 
ticulars, the sixth molar cannot be confounded with the others, 
and therefore its existence in the mouth is quickly detected. 
The general condition of all the teeth about this time is de- 
picted in fig. 28. We have here one-half of the lower jaw dis- 
sected in order to show the number and position of both tem- 
porary and permanent sets of incisors and molars. The three 
temporary molars are still in situ, but lying beneath their fangs 
are the corresponding permanent teeth 1, 2, 3, contained within 
their capsules. From the central part of each temporary tooth a 
portion of membrane contracted into the form of a small band ex- 
tends to the capsule below, supporting it as by a pedicle. These 
elongated portions of membrane have been designated the giiber- 
nacula, the guides or directors of the teeth into the proper passage. 
Todd and Bowman, describing the wisdom of design, which is 
observable in every stage of the process of development of the 
teeth, very truly observe — 
" It has been supposed that the elongated productions of the cavities of re- 
serve, which have been carried down from the surface with the permanent 
