276 The Teeth of Fishes. [Sess. 
The first premolar is rudimentary. The incisors are peculiar 
on account of a folding in of the enamel in the centre, forming 
the well-known pit or mark by which a horse’s age can be 
reckoned with certainty up to a certain time. The pit or 
mark is situated near the middle of the cutting edge of the 
teeth. It is shallow, and by the constant rubbing of the 
upper and lower teeth together, it is obliterated in the two 
centrals at 6, in the laterals at 7, and on the next from 8 to 
10 years. If a horse is fed on soft food, the mark will not 
be rubbed out so soon as if it had been reared on hard food. 
When the horse is about 10 years old a groove commences to 
show at the gum margin of the outermost incisor, and as the 
teeth are being constantly pushed from their sockets to make 
up for the attrition, the groove lengthens as well as the tooth, 
and when it has reached the middle of the crown the horse is 
14, and by the time the cutting edge is reached the horse is 
reckoned 21. The thickness of the incisors also varies, by 
which means one can get a fair idea of a horse’s age. 
The incisors of the pig are peculiar, on account of their 
being widely separated at their bases. The molars are adorned 
with rounded conical cusps called the Bunodont pattern. 
In the hippopotamus the dental formula is— 
We Rg ee 4 
1.35645; p.m. 4; m 2 
belo 
The incisors are long and tapering, while the canines are 
enormous teeth, and are used by the animals for uprooting 
aquatic plants on which they feed. The ivory is of dense 
substance, and is used for the manufacture of small objects. 
The principal feature in the dentition of the carnivora is 
the very small incisors and powerful canines, with the pre- 
molars narrow and pointed, and as a rule rudimentary molars. 
The fourth upper premolar is called a carnossial tooth, and 
the first molar in the lower. 
We now come to the aquatic carnivora, or seals and walruses. 
The Otariide, or Sea Lions, are the seals from which sealskin 
is procured. Their teeth are like the cetacean, not differing — 
much from one another in any part of the mouth. The Phoca 
Greenlandica is the seal commonly met with round our coasts. — 
The walrus has enormous upper canines. Its dental formula is— — 
eg OUP RS a or 
1355 +3 pm F 
“= Ae ae MND rade td 2: 
seer. 
