248 STRUCTURE AND ADAPTATION OF TEETH 



The front teetli of the horse are remarkable for 

 furnishing a test whereby the age of the animal 

 may for several years be determined. (Fig 43.) 

 The " mark," as it is popularly called, is caused 

 by an oblong fold of enamel which dips down into 

 the crown of the tooth, from the cutting surface 

 to the commencement of the fang. This fold of 

 enamel encloses a column of cementum, the surface 

 of which, from its softer nature, is always worn 

 below the ring of enamel, and becomes stained by 

 the food. 



As the horse advances in age, the constant 

 attrition wears out the mark from the incisors, 

 commencing from the central pair, proceeding in 

 the second and third pairs, successively, and still 

 later in the upper incisors also, until, in an aged 

 horse, the entire depth of enamel is worn away. 

 The true " mark " has now disappeared, a spot of 

 the dark underlying cement alone indicating its 

 former position. 



The molar teeth, which in their compound 



Fig. 44. — DeciJuons and perwanetd Molars. JJjiper Jaw of two-year 

 old Colt. {From Professoi' Oicen.) 



