UNKELIABLE MARKS. 751 



already indicated, are really only four-year-olds. Such animals, 

 instead of liaving the cutting surfaces of the corner incisors of both 

 jaws fully in wear, on the inside as well as on the outside of the 

 tooth, very rarely show any w^ear of the upper corner incisors at 

 the time mentioned. 



Teeth which Retain the Mark and Central 

 Enamel Beyond the Ordinary Time. 



The depth of the cavity on the tables of the incisor teeth 

 varies considerably in different horses, and even in particular 

 pairs of teeth, in the same mouth. The thickness of the layer 

 of cement lining these cavities, is also, as we have seen on p. 742, 

 subject to much variation. Hence, it is not at all uncommon 

 to meet with mouths, the " marks ^^ in which indicate that the 

 animal is "younger" than he really is; that he is "younger" on 

 one side of his mouth than on the other ; or that one or more teeth 

 retain these cavities to an unusually late period. The varying 

 hardness of the teeth and of the forage, naturally contribute to 

 irregularity in the amount of wear. In less frequent oases, the 

 marks disappear earlier than usual. It is not a, very rare occurrence 

 to observe that the mark has disappeared out of the lateral lower 

 incisors in a six-year-iold animal. These considerations render the 

 " mark," of itself, anything but a safe guide to the determination 

 of a horse's age. The roundness of the tables of the lower central 

 incisors, and, to a less degree, of the lateral ones; the oval 

 appearance of the tables of the comer incisors ; the shortness and 

 central jDosition of the dental star; the smallness of the central 

 enamel of the lower central teeth, and its closeness to the posterior 

 edge of the table ; the obliquity of the teeth, as viewed in profile ; 

 and the flatness of the curves of the incisor teeth will afford un- 

 erring proofs that the animal ought to be " beyond mark of mouth," 

 namely, over eight years. 



Retention, for an unduly long period, of the apex of the cone of 

 the central enamel of the permanent incisors, gives a false appear- 

 ance of comparative youth to the mouths of some horses. This, 

 of course, occurs only after the cavity (or " mark ") has dis- 

 appeared ; ■ and is due to the fact of the solid apex of the cone of 

 enamel being deeper than usual; to the hardness of the teeth 

 themselves ; or, to some extent, to the soft nature of the food. 

 The form and degree of obliquity of the incisors, and the position 

 and extent of the dental star, will serve as guides from which to 

 draw correct deductions as to the age. 



