The mark in the tooth is occasioned by the food blackening the hollow pit. This is formed on the surface by the bending in of the enamel, which passes over the surface of the teeth, and, by the gradual wearing down of the enamel from friction, and the consequent disappearance of it, the age can be determined for a period of several years.
The disease is caused by the ray fungus. The result is local tumors in the bones and other tissues.]
When a horse has attained his sixth year the mark on the central or middle incisors or nippers of the lower jaw will be completely worn off, leaving, however, a little difference of color in the center of the teeth. The cement which fills the hole produced by the dipping in of the enamel will be somewhat browner than that of the other portions of the tooth, and will exhibit evident proofs of the edge being surrounded by enamel.
At seven years the marks in the four middle incisors are worn out and are speedily disappearing in the corner ones. These disappear entirely at the age of eight; thus all marks are obliterated at this age on the lower jaw; the surface of the teeth are level and the form of the teeth changes to a more oval form.
The marks on the upper jaw are still present, since there has been less friction and wear on them. At nine the marks disappear from the central upper incisors, at ten from the adjoining two, and at eleven from the corner teeth.
To tell the age of the horse beyond this period is difficult and uncertain, except by those very much experienced in performing the undertaking. The shape of the teeth, the color and the condition all enter into the determination but there is no fast and fixed rules after the marks have disappeared.
Cattle have no incisor teeth on the upper jaw. They have eight incisors on the lower jaw. According to Mayo, the temporary incisors are as follows: “The central incisors or nippers are up at birth, the internal lateral at one week old, the external lateral at two weeks, and the corner incisors at three weeks old. They are replaced by permanent incisors approximately as follows, though they vary much more than in the colt: The central incisors are replaced at 12 to 18 months; the internal laterals at about two and a half years; the external laterals at three to three and a half years; and the corner incisors at about three and a half years. In the horned cattle, a ring makes its appearance at three years of age, and a new ring is added annually thereafter.”