55 



long, though in rare instances they are worn down 

 almost to the gums. When long, they will generally 

 show interstices dividing them, such interstices, how- 

 ever, not being free, but occupied by a compact mass 

 of foreign matter, derived from the food, and having 

 a black colour. The reader will, by turning to the 

 coloured plates of twenty and thirty years, see these 

 accumulations indicated. When the incisors are very 

 short, they are arranged in a different order to those 

 of the young animal. The tables of the teeth of the 

 young horse, form almost a semi-circle ; in the adult 

 animal, they gradually assume a crescentic order, and 

 as age progresses, they ultimately range, more or 

 less, in a straight line. The teeth also look narrower 

 as the fangs descend with the wear of the organs, and 

 in colour they slightly change. The enamel loses 

 much of its semi-opaque and characteristic appear- 

 ance, assuming a more dull aspect, and a yellowish 

 tint. The crusta petrosa is to be seen only near to the 

 gums, and within the grooves, which often are deep 

 and very well defined, and within which the remains 

 of the once-investing membrane becomes almost black. 

 Then again, the tables themselves change their shape 

 as the years increase. At first, these surfaces are of 



