22 THE HORSE AND ITS RELATIVES 



horses whose ancestors have for many generations 

 been accustomed to feed on hard and tough grasses 

 will show a greater degree of cranial deflection than 

 those whose food has consisted either of softer and 

 more easily yielding herbage or of grain. More- 

 over, it seems highly probable that the degree of 

 deflection may vary with age — the older the 

 animal, the greater the degree of bending. This, 

 indeed, is exemplified in the case of two skulls 

 figured by Professor Ewart on plate ii. of the 

 memoir cited in the footnote to illustrate this 

 feature ; the one shown in the upper figure of that 

 plate, in which the deflection is slight, being 

 obviously that of a young animal, while the one in 

 the lower figure, which displays the bending in a 

 very marked degree, is as clearly that of an aged 

 horse. 



Yet another cranial feature remains to be 

 noticed. In the skulls of certain domesticated 

 horses, especially Arabs, thoroughbreds, and shires, 

 a more or less distinct oval or circular depression 

 may be noticed a short distance in front of the 

 socket of the eye, or orbit, and therefore con- 

 veniently called the preorbital depression. It is 

 shown faintly in the figure of the skull of a shire 

 horse in plate iv. fig. i, and more clearly in the photo- 

 graph of the skull of a quagga (plate iv. fig. 2) ; the 

 latter instance shows that the feature is not confined 

 to the horse itself. Of itself, this feature may seem 



