192 
MAMMALIA. 
years and a half to four years the intermediate fore- teeth expe- 
rience the same change, and the lower tushes begin to make their 
appearance. The corner -teeth are also renewed when between four 
and a half to five years; the upper tushes likewise pierce the gums, 
and about the same date the sixth grinder shows itself. 
A depression, or small hollow, may be noticed on the surface of 
the crown of the second growth of fore- teeth, just as in the milk- 
teeth, and these hollows are gradually worn away in the same 
fashion. 
The pincers of the lower jaw lose their cavities when the Horse 
is five or six years old ; the intermediate fore- teeth are the next 
to raze. The marks in the corner -teeth are obliterated at the age 
of seven or eight years. The process of destruction of the marks 
in the upper fore-teeth goes on in the same order, but more tardily. 
(Figs. 51 and 52). 
When all these various changes have taken place, the Horse is 
looked upon as aged (Fig. 53), because the teeth no longer furnish 
any certain indications as to the age of the animal. Only 
approximate inferences can now be drawn from the length and 
colour of the tusks, which become more and more bare and 
projecting from the gum, &c. 
The domestication of the Horse appears to date back to the very 
earliest period of his appearance on earth ; and as this animal 
adapts itself to every necessity, every want, and every climate, 
its subjection has resulted in a considerable number of races, 
distinguished by more or less prominent characteristics of shape, 
strength, temper, and endurance. Although generally intelli- 
gent, affectionate, and endowed with considerable powers of 
