[Illustration: MONTH.] [Illustration: FIVE TO EIGHT MONTHS.] [Illustration: TEN MONTHS.] [Illustration: TWELVE MONTHS.] [Illustration: FIFTEEN MONTHS.] These teeth are temporary, and are often called milk-teeth. Their edge is very sharp; and as the animal begins to live upon more solid food, this edge becomes worn, showing the bony part of the tooth beneath, and indicates with considerable precision the length of time they have been used. The centre, or oldest teeth show the marks of age first, and often become somewhat worn before the corner teeth appear. At eight weeks, the four inner teeth are nearly as sharp as before. They appear worn not so much on the outer edge or line of the tooth, as inside this line; but, after this, the edge begins gradually to lose its sharpness, and to present a more flattened surface; while the next outer teeth wear down like the four central ones; and at three months this wearing off is very apparent, till at four months all the incisor teeth appear worn, but the inner ones the most. Now the teeth begin slowly to diminish in size by a kind of contraction, as well as wearing down, and the distance apart becomes more and more apparent. [Illustration: EIGHTEEN MONTHS.] From the fifth to the eighth month, the inner teeth will usually appear as in the cut of the teeth at that time; and at ten months, this change shows more clearly, as represented in the next cut; and the spaces between them begin to show very plainly, till at a year old they ordinarily present the appearance of the following cut; and at the age of fifteen months, that shown in the next, where the corner teeth are not more than half the original size, and the centre ones still smaller. [Illustration: TWO YEARS PAST.]