34 



however, shows that the enamel dips deep into 

 the substance of the ivory, and indicates what would 

 have been the form of the infundibula, had not the 

 crusta petrosa filled up the cavities. The infundibula 

 have received special attention from horsemen, and 

 have been thought to indicate correctly the age of 

 the horse ; their lining membrane speedily becomes 

 blackened by the chemical action of the food, &c., 

 constituting what are called the " marks " of the 

 mouth ; and as the teeth undergo wear, these marks 

 are ultimately lost. The period at which they may 

 disappear, and the appearances which they may put 

 on, are well shown in a plate which Mr. Fores has 

 published, entitled " The Age of the Horse,'' and 

 to that plate I therefore refer the reader ; but, while 

 doing so, I must caution him not to depend too 

 much upon a sign, which is only true as a general 

 rule ; for as the infundibula in all animals are not of 

 the same depth, or supposing them to be of one 

 depth, the crusta petrosa is seldom of the like thick- 

 ness in any two horses, and the teeth do not wear 

 uniformly in different subjects, of course the indi- 

 cations they exhibit cannot be absolutely relied upon. 

 Those indications, however, ought to be known, and 



