120 THE STRUCTURE OF THE HORSE. 



maturation of the latter, and especially while the 

 jaws are acquiring size and strength sufficient to 

 support them. In all cases these teeth disappear (by 

 the absorption of their roots and shedding of the 

 crowns) before the frame of the animal has acquired 

 complete maturity. As the first set of teeth are, as 

 a general rule, present during the period in which 

 the animal is nourished by the milk of the mother, 

 the name of " milk-teeth " (French, dents de lait; Ger- 

 man, Milchzahne) has been commonly accorded to 

 them, although it must be understood that the time 

 of their duration has nothing to do with that of lac- 

 tation. "Temporary teeth," or "deciduous" teeth, 

 are, perhaps, therefore, better names. No mammal 

 has more than two sets of teeth. 



Special Characters of the Teeth of the Horse. — In- 

 cisors. — To return to the teeth of the horse. The 

 incisors, or " nippers," as they are called in veterin- 

 ary language, of each jaw, are placed in close con- 

 tact, forming a semicircle. The crowns are very 

 large, somewhat chisel-shaped, and of nearly equal 

 size. They have all a peculiarity not found in any 

 other existing mammal,* and seen only in the 

 Equidce of comparatively recent geological forma- 

 tions. In the most primitive species these teeth 



* Macraiichenia, an extinct South American Perissodac- 

 tyle, had somewhat similar incisors. 



