Fig. 22. Fifteen months.
From the fifth to the eighth month the inner teeth will usually appear as in [Fig. 19]; and at ten months this change shows more clearly, as in [Fig. 20], and the spaces between them begin to show very plainly, till at a year old they ordinarily present the appearance of [Fig. 21]; and at the age of fifteen months that shown in [Fig. 22], where the corner teeth are not more than half the original size, and the centre ones still smaller.
Fig. 23. Eighteen months.
Fig. 24. Two years past.
The permanent teeth are now rapidly growing, and preparing to take the place of the milk-teeth, which are gradually absorbed till they disappear, or are pushed out to give place to the two permanent central incisors, which, at a year and a half, will generally present the appearance indicated in [Fig. 23], which shows the internal structure of the lower jaw at this time, with the cells of the teeth, the two central ones protruding into the mouth, the two next pushing up, but not quite grown to the surface, with the third pair just perceptible. These changes require time; and at two years past the jaw will usually appear as in [Fig. 24], where four of the permanent central incisors are seen. After this the other milk-teeth decrease rapidly, but are slow to disappear; and at three years old the third pair of permanent teeth are but formed, as in [Fig. 25]; and at four years the last pair of incisors will be up, as in [Fig. 26]; but the outside ones are not yet fully grown, and the beast can hardly be said to be full-mouthed till the age of five years. But before this age, or at the age of four years, the two inner pairs of permanent teeth are beginning to wear at the edges, as shown in [Fig. 26], while at five years old the whole set becomes somewhat worn down at the top, and on the two centre ones a darker line appears in the middle, along a line of harder bone, as appears in [Fig. 27].
Fig. 25. Three years past.