652 THE EXTERIOR OF THE HORSE. 



Second Period. — Levelling and Progressive Wear of the 

 Incisors of the First Dentition.— About One Year. — The cor- 

 ners are well emerged through the gums, but the inferiors have not yet 

 come in contact with the superiors. The inferior pincers, if not levelled, 

 are much worn upon their two borders ; the incisive arcade com- 

 mences to be slightly depressed at their level. The superior pincers 

 and the intermediates are scarcely worn through upon their posterior 

 border. (Plate VIII.) 



About Sixteen Months. — The superior corners are in. apposition 

 with the inferior, and have commenced to wear, in both jaws, by their 

 anterior border which touches the intermediates ; their necks are quite 

 visible above the gums. The inferior pincers are often, at this time, 

 completely levelled, but in the intermediates this is much more rare. 

 In the upper jaw the table of the two sorts of teeth is completely 

 formed ; the depression of the incisive arch is present. (Plate IX.) 



About Twenty Months. — The inferior corners are much worn 

 over the whole extent of their anterior border ; the superior corners 

 show the wear a little less. The inferior pincers become more con- 

 stricted at their base and are completely levelled ; the intermediates are 

 often levelled. Ordinarily, the incisive arch is still less convex. 

 (Plate X.) 



About Two Years. — The inferior dental arcade is completely 

 worn down to the level of the pincers and the intermediate teeth ; the 

 superior arcade is less worn. The neck of the superior pincers is above 

 the level of the gums. Pressure on the palatine arch posterior to these 

 teeth shows a sensitiveness of the gums, and reveals the presence of 

 the permanent incisor underneath the mucous membrane. The inter- 

 mediate teeth commence to show their necks, above and below. Finally, 

 the incisive arcade becomes wider transversely, and is much flattened 

 in its central portion. (Plate XI.) 



It can be seen from the preceding characters that the levelling of 

 the milk-teeth does not furnish as precise an index as Girard would 

 seem to indicate. According to this author, in fact, " the pincers should 

 always be levelled at ten months, the intermediate teeth at one year, and 

 the corners at from fifteen to twenty-four months." Unfortunately, 

 there are too many allowances to be made in this respect, for these 

 changes follow each other with much less regularity. Some variations 

 result, as we know, from the thickness of the nucleus of cement 

 which occupies the bottom of the external dental cavity ; they depend 

 also upon the character of the food and the manner of existence of the 

 animals. 



