AGE, AS INDICATED BY THE TEETH. 417 



or third temporary molar is similarly replaced ; and about the same time 

 the last or sixth permanent molar begins to appear. Thus when the 

 mouth is completed, there are six permanent molars in each jaw, or 

 twenty-four in all. 



These structural changes afford a very good index of the age of the 

 horse up to the period when they are completed, namely four years old. 

 The Molars, however, are sejdom referred to, because their position at 

 the back of the mouth renders their examination inconvenient and often 

 very difficult. Nevertheless, it is useful to be acquainted with the struc- 

 tural changes of these teeth in cases where there may be a doubt as to the 

 true age as indicated by the incisors. After four years old, the molars 

 are not often taken into consideration in determining the age of the horse. 



We may mention in passing, that a supplementary molar known as a 

 " Wolfs tooth," sometimes appears in either jaw. Such teeth seldom 

 cause any inconvenience. If they do so, they can easily be removed by 

 the pincers, as they are only of a rudimentary character. 



867. Of the Anterior teeth or Incisors. 



The Anterior teeth, or Incisors, are six in number in each jaw, when 

 the mouth is complete ; and in the immediate rear of these in males, 

 there is usually added one very peculiar pointed tooth on each side in 

 each jaw, called a tusk. Though there are two crops of incisors, yet 

 there is but one of tusks. In fact, these teeth, though they begin to 

 appear about four years old, are not usually fully developed until the last 

 permanent incisor is more or less up. 



For the sake of brevity we shall confine our remarks to the lower jaw, 

 as the structural changes, which take place in the upper, are nearly 

 similar. In passing, however, we may remark that the upper incisors 

 are considerably longer and larger than the lower. 



868. Distinction between Temporary and Permanent Incisors. 



Temporary, otherwise called Milk (Plate 39), are easily distinguished 

 from Permanent incisors by the following well-marked signs, namely, 

 they are smaller, whiter, and have more distinct necks. They are smooth 

 externally, and grooved on the inside, probably in order to enable the 

 foal more easily to grip the teats of the dam. Their fangs are small and 

 have but little attachment to the giflns. The jaws are plump, fleshy and 

 round, and the teeth are arranged in something like a semicircle. 



Permanent teeth, on the other hand, are larger, broader, wider in their 

 necks, grooved externally and smooth internally, and more discoloured 

 than milk teeth. The discoloration is due to the lodgment of the juices 

 and other matters connected with the food in the grooves. The object 

 of the external grooving probably is to enable the animal to get a better 

 grip on grass and such like food. The plumpness and circularity of the 

 jaw is less than in the younger animal, and it gradually decreases, until 

 in very old age the teeth are arranged in a nearly straight line. 



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