of the Animals of the Farm. 
passing from the elliptical, to the oval, the square, and the triangle, 
first with equal sides, and then with two sides longer than the base. 
For the purpose ot making tlie nature ot these changes evi<lent, 
the outlines of the figures, which result from the wear of the 
tooth-structures, are placed on the right of the tooth (Fig. 2). 
There are, however, other points which require to be noticed. 
The cavitv in the centre of the table is formed by an inflexion 
of the structures of the tooth in the shape of a hollow cone, 
the apex of which reaches into the fang. In the recent tooth 
the cavity extends quite across the table, but, necessarily, as 
the tooth is worn it becomes more and more circumscribed, 
and at length the apex of the hollow cone is reached, and the 
" mark " consists of a mere spec, and then is entirely obliterated. 
Owing to the inflexion of the whole of the tooth-structures to 
form the hollow cone, the tables of the incisors have, besides the 
ivory and crusta, two distinct rings of enamel, which are distin- 
guished from the other parts by their pearly whiteness, an external 
or larger ring which forms the outline of the table, and a central 
ring which surrounds the cavitv in the centre of the table. That 
part of the tooth which is situated in the front of the mark is 
described as the anterior edge, and the portion behind it as the 
posterior edge. 
All these parts are indicated in the diagram (Fig. 2), and it 
is necessary that the reader should clearly recognise them, in 
order to understand the description of the changes which are 
occasioned by the wear to which the teeth are subjected. 
\\ hile the temporary dentition is proceeding, and also during 
the time that the permanent are taking the places of the 
temporary teeth, the examiner may form an opinion of the age 
by merely noting what teeth are in the mouth ; but when these 
changes are completed, he is compelled to base his conclusion 
upon the evidence which he gains from an inspection of the 
tables of the incisor teeth ; those of the lower jaws being 
always selected. In doing this, he has to observe whether the 
cavity or mark extends across the tooth, or is surrounded by a 
line of worn structure, in which case the table is said to be 
fully formed, as it appears in Fig. 2. The width of the worn 
. surface in front of the cavity, as compared with that at the 
back, will be taken into consideration, and also the shape of 
the table, whether oval, or approaching the square, or triangular. 
No particular importance can be attached to the tusks as a 
means of judging the age, they only occur in the horse, and are 
less regular than the other teeth in the time of their eruption. 
The small rudimentary teeth which sometimes exist in the 
place of tusks in the mare must not be taken into account at all. 
There may in certain cases be reason to suspect that the mouth 
