NUMBER AND ARRANGEMENT 



391 



a.- 



in fig. 600 the temporary and permanent incisors of the horse are shown 

 side by side. 



No difficulty could possibly be experienced when the two orcans are 

 removed from the jaw for the purpose of examination — the difference in 

 form and size is quite apparent; but it may also be noticed that the 

 permanent incisor decreases in width from above downwards, without 

 showing any line of separation between the upper part of the tooth which 

 is called the crown, and the lower part, or fang. In the temporary incisor 

 the distinctive boundary between the two 

 parts is perfectly well defined. These 

 differences are not quite so well marked 

 when the teeth are looked at in the 

 mouth of the living animal, but the 

 small size of the crown, and the absence 

 of deep grooves in the temporary incisors, 

 will be sufficient to enable the observer 

 to distinguish the one from the other 

 during the period of change from tem- 

 porary to permanent teeth. It is not, 

 however, quite so easy to distinguish 

 the temporary from the permanent in- 

 cisors in ponies between one and two 

 years of age, as these animals very fre- 

 quently present some of the adult char- 

 acter in their general conformation; and 

 when the judgment is to be formed en- 

 tirely by an examination of the teeth, it 

 is quite possible for one who is not an 



expert to mistake a well-developed pony of one year old for a five-year-old, 

 and one of two years old for a six-year-old. 



The difficulty, however, may be at once disposed of by an examination 

 of the molar teeth. 



To appreciate the variations which take place in the outline of the 

 worn surfaces or tables of the incLsor teeth as age advances, it is desirable 

 that the examiner should have a clear understanding of the peculiarities 

 of form in these organs, which render a certain fixed series of changes in 

 the outline of the tables quite inevitable. In the next figure (fig. 601), 

 representing a permanent incisor of a horse, it will be seen at once that 

 the long diameter of the table is exactly at right angles with the long 

 diameter at the base of the tooth. Further, it will be seen in the drawing, 

 which shows the tooth as seen from the back, that a ridge extends from 



Fig. 601. — Permanent Incisor, showing sections 

 at various points, a, Tlie central cavity. 



