THE DIGESTIVE SYSTEM 75 



twenty-one years old. The infundibulum gradually becomes 

 smaller, nearer the lingual border, and finally disappears. It 

 remains longer in the upper than the lower incisors because of its 

 greater depth; therefore the latter should be observed when 

 determining the age of a horse. 



Pig. 21. — Skull of ox two years of age, sculptured to show the embedded parts 

 of the teeth: Jl-4, permanent incisor teeth, the third and fourth not erupted ; 

 Di3, 4, third and fourth deciduous incisors; Pl-3, upper permanent premolars, 

 only first erupted; Dp 2, 3, deciduous premolars; Ml-3, molars. (Sisson, 

 Anatomy of Domestic Animals.) 



The formula for the permanent teeth of the ox is: 

 0„0 „3 „,3\ 



>mn»()-» 



The ox has no incisors in the upper jaw (Fig. 21). There are 

 eight incisors in the lower jaw. They are simple teeth without 

 infundibulum so present no cup. The crown is white, short, and 



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