TEETH.

Teeth are objects situated in the upper and lower jaws. They are made of the same tissues as bone but contain 10¹⁄₂ per cent. more of earthy salts. This fact accounts for their extreme hardness. Unlike bone they can stand exposure to air and friction without becoming diseased. Teeth are used to masticate or chew the food, and because of the constant change in their formation and appearance they serve as a guide in telling the age of the horse.

There are three hard structures that enter into the formation of the teeth—Dentine or Ivory, Enamel, and Cementum, or Crusta Petrosa.

The Dentine, or ivory, is situated in the upper part around the pulp or nerve cavity. It is of yellowish color and largely supplied with nerves which pass through it from the pulp cavity.

The Enamel is the hardest substance of the tooth, and covers the outside of all the exposed part. This substance is characterized by its whiteness and, unlike the dentine, contains no blood vessels or nerves. If part of the enamel is broken off it is never replaced, and the tooth below the broken part generally becomes decayed.

The Cementum, or crusta petrosa, is found in the fang or root and the parts situated below the gum. It is the softest part of the tooth.

Teeth may be simple or compound. Simple as in the dog, where the entire exposed surface is covered by a solid cap of enamel, which alone is in wear; compound or complex, as in the horse, where various tissues are in wear. A tooth consists of the following anatomical parts: The body, or crown, that part above the gum; the table, the part that comes into wear on the top; the neck, the part to which the gums are attached; and the fangs or roots, the parts situated down in the bone.

There are three kinds of teeth found in the horse, the incisors, the canine and the molars.

The Incisors, or front teeth, situated in the front part of the mouth just inside the lips, are twelve in number, six above and six below.

The Canine, or bridle teeth, are often absent in the mare. They are four in number, two in the upper and two in the lower jaw, one on each side about two inches back from the incisor teeth. They are from a quarter to three-quarters of an inch above the gum, are round and pointed and of no particular use. They resemble the eye teeth of other animals.

The Molars, or back teeth, are twenty-four in number, six on each side in the upper and six on each side in the lower jaw. With these the food is ground and masticated.

Wolf Teeth are two small, round, pointed temporary teeth which vary in size in different animals, situated one on each side in front of the molars or back teeth in the upper jaw.

Temporary and Permanent Teeth.—The horse has two sets of teeth. The milk are temporary and are those that the colt sheds; while those that come in and remain without being shed are called the permanent teeth. The cutting of the teeth of the foal varies, but at or within nine days after birth he has four front teeth, two in the center above and two below, and in the back part of the mouth twelve molars. At from seven to nine weeks four more incisors or front teeth appear, one at each side of the two center teeth in each jaw. At nine months he gets the last of his milk or temporary teeth, these being the corner teeth, two in the upper side and two in the lower side of the jaw. At this time he has his full set of milk temporary teeth, consisting of twelve molars or grinders and twelve incisors or front teeth, six above and six below, making twenty-four in all. As the colt advances in age he sheds all these teeth. He then commences to get permanent teeth. When the age of one year is reached, four permanent molars appear, two in each jaw, one on each side, behind the three temporary teeth. At two years of age he gets four more back molars, one on each side of each jaw. When the age of two years and nine months is reached the two middle teeth of the temporary incisors, or front teeth of each jaw fall out, and are replaced by two permanent incisors in each jaw; thus at the age of three years these four permanent incisors are up and in wear. At this age, the first eight molars, two on each side of each jaw, are shed and replaced by eight permanent molars. At four years of age he sheds four more front or incisor teeth next to those shed at three years, and these are replaced by four more permanent incisors or front teeth. At this age, too, he sheds the four remaining temporary molars, or grinders, which are replaced by four more permanent molars. He also gets four more permanent molars at the back of the mouth. Thus at the age of four years the colt has a full set of permanent molars, consisting of six on each side of each jaw, making twenty-four in all. At five years of age he sheds the four remaining temporary incisors or front teeth, which are replaced by four permanent incisors, known as the corner teeth. It is important to become familiar with the time at which the colt sheds his different teeth, for sometimes the caps or shells of the teeth do not fall off when they should. These should be watched, for they greatly interfere with feeding and should be removed with forceps. At five years of age the canine or bridle teeth make their appearance; thus at the age of five years the colt has all his teeth or what is known as a full mouth.

The following table shows the various changes taking place in the mouth of the horse from the time of birth up to the age of five years:

Hence the horse has—

	—Incisors—		Canine	—Molars—
Age	Temporary	Permanent		Temporary	Permanent
At or soon after birth	4	0	0	12	0
9 weeks	8	0	0	12	0
1 year	12	0	0	12	4
2 years	12	0	0	12	8
3 years	8	4	0	4	16
4 years	4	8	0	0	24
5 years	0	12	4	0	24=40

The table given below indicates the various changes which occur in the mouths of ruminants, and more particularly in the mouth of the ox:

RUMINANTS

	—Incisors—			—Molars—
Age	Temporary	Permanent	Age	Temporary	Permanent
At or soon after birth	4	0		12	0
2 weeks	6	0	1 year	12	4
3 weeks	8	0	2 years	8	12
2 years	6	2	3 years	4	16
3 years	4	4
4 years	2	6	4 and 5 years	0	24=32
5 years	0	8

A table giving the number and variety of teeth as they occur in the domestic animals and in man may be serviceable as one of handy reference, and is herewith appended:

	Incisors	Molars	Canine	Bicuspid	Total
Man	4 — 4	6 — 6	2 — 2	4 — 4	= 32
Horse	6 — 6	12 — 12	2 — 2	0 — 0	= 40
Ox	0 — 8	12 — 12	0 — 0	0 — 0	= 32
Dog	6 — 6	12 — 14	2 — 2	0 — 0	= 42
Pig	6 — 6	14 — 14	2 — 2	0 — 0	= 44
Cat	6 — 6	8 — 6	2 — 2	0 — 0	= 30

The dental formula of the ox is the same as that of all ruminants.