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tooth be observed, a cavity will be seen in the centre 

 of it : this cavity, called the infundibulum, is of 

 variable depth. In the temporary or milk teeth, it 

 extends only half way down the crown ; in the per- 

 manent or horse incisors, it is from three quarters 

 of an inch to an inch and a quarter deep, being of 

 greater depth in the teeth of the upper than in those 

 of the lower jaw, and not of the same magnitude 

 in all horses. The infundibula are indentations in 

 the body of the ivory, and they possess two co- 

 verings, an external one of crusta petrosa, and 

 internal investment of enamel : the enamel does not 

 materially vary in thickness upon this part, but the 

 crusta petrosa of the infundibula is, in different sub- 

 jects, of very unequal extent. In some animals it 

 becomes very thick, and in such, the infundibula 

 seem soon to be obliterated, owing to the crusta 

 petrosa filling up the cavity. A good specimen of 

 the early obliteration of the cavity, by the thickness 

 of its investing membrane, is shown by the teeth 

 preserved with the jaw of the horse Leander, 

 which is now in the possession of Mr, W. Field. 

 That animal, though but four years old, had lost 

 the " marks " in the central incisors. A white line, 



D 



