418 OHAPTEE 58. 



869. Of the Temporary or Milk Incisors. 



The foal is born with his teeth in a rudimentary state in the gums. 

 At various periods during the first ten months the different temporary 

 incisors appear (Plate 39, figure 0). Under one year old the foal is also 

 clearly distinguished by a woolly tail. 



The yearling is complete in all six incisors, but several well-marked 

 signs distinguish his mouth from that of the two-year-old. The teeth at 

 this period show but little signs of wear. The corner teeth are mere 

 shells, having no inner walls, and all the teeth are in close juxtaposition. 

 (Figure 1.) 



At two years old, the inner wall of the corner teeth has grown up level 

 with the outer wall. The centre teeth show considerable signs of wear, 

 and indeed all the teeth appear somewhat smaller than they did in the 

 yearling. They also stand somewhat wide apart at their necks on account 

 of the gradual growth of the jaw in width. (Figure 2.) 



Inexperienced persons have been known to mistake a two-year-old for 

 a five-year-old mouth. But the difference in the conformation of the 

 animal, as well as of milk and permanent teeth (see par. 808), ought to 

 make such a mistake impossible. 



870. Development of tlie Permanent Teeth. 



A few months before three years old, the horse sheds the two centre 

 milk teeth, which are replaced by permanent. Thus the jaw contains at 

 three years old two centre permanent teeth and two milk teeth on each 

 side. (Figure 3.) 



A few months before four, the horse sheds the two next milk teeth, 

 which are replaced by permanent. Thus the jaw now contains four per- 

 manent and one milk tooth on each side. (Figure 4.) The appearance 

 of the mouth when closed, and also the mode in which the teeth meet, 

 are shown in figure 4 a. This figure will be presently contrasted with 

 figures 26 and 27, which show the mode in which the mouth closes and 

 the teeth meet in extreme old age. 



A few months before five, the horse sheds the two remaining milk 

 teeth, which are replaced by permanent. Thus the jaw is now furnished 

 with six permanent incisors, but the corner teeth are mere shells, having 

 no internal wall. The absence of this wall distinguishes the five from the 

 six-year-old mouth. (Figure 5.) 



A few months before six, the inner wall of the corner teeth has grown 

 Mp level with the outer wall. (Figure 6.) 



The mouth is now fully complete in incisors, and no further structural 

 changes take place in them. As a general rule, we may add that the 

 upper temporary teeth fall out a little before those in the lower jaw. 



Up to six years old, therefore, inasmuch as we have structural changes 

 to guide us, there can seldom be any doubt as to the age of the animal. 

 There are, however, some well-authenticated instances of abnormal deve- 

 lopment of the permanent incisors, but they are rare. 



Thoroughbred horses date their age from the 1st of January, whilst 



