THE TEETH. 71 



tough, and of a yellowish colour, not so dark as the crusta 

 petrosa, but much darker than the enamel, which last is 

 perfectly white. It has an opening at the point, or bottom 

 of the fang, which leads to a cavity that contains the vessels 

 and nerves that nurture the substance of the tooth, as well 

 as endow it with feeling. 



Now, when we properly consider the services to which 

 the horse's teeth are put, viz. to nipping off and grinding 

 up the food, the use of these three substances is perceived. 

 The enamel, which is brittle as glass, yet being firmly en- 

 closed between two tough substances, is preserved from 

 chipping or breaking ; but being protected acts with the 

 efficiency of steel. It is usually the least worn of the 

 three materials that enter into the composition of the tooth, 

 projecting comparatively far beyond them, 



A tooth is divided into fang, neck, and crown. The fang- 

 is placed in the jaws, and fixed firm into certain cavities in 

 the bones of each jaw ; whence it is propelled upward into 

 the mouth as age advances, the lower part of the cavity 

 closing up as the fang enters the mouth. The fangs then 

 form the teeth of very old horses ; upon this the enamel 

 being in parts deficient, and where it exists very thin, we 

 can easily see a reason why the teeth of old horses, com- 

 posed almost entirely of crusta petrosa and bone, should 

 appear yellow or discoloured. 



The neck is that part of the tooth which narrows as it 

 meets the gum, the point of narrowing being termed " the 

 neck.'" There is no neck to be discovered in the perma- 

 nent, but it is well marked in the temporary teeth. 



The crown is that part of a tooth which can be seen by 

 a spectator upon opening the mouth. Thus, as age pro- 

 gresses, and part of the fangs are pushed into the mouth, 

 every portion of a fang so projecting from the gum becomes 

 the crown of a tooth. 



The teeth of the horse have been thought to be endowed 

 with growth to meet the wear of years ; so undoubtedly 

 they are, but not to the extent that has been imagined. 

 The chief loss of substance is supplied by the cavity in 

 which the fang is situated becoming more shallow, and thus 

 pushing down, or lifting up, the tooth into the mouth. 



The double teeth of the horse perform the office of 



