24 THE HORSE AND ITS RELATIVES 



but must have been derived from some other form 

 in which such a specialisation had been developed. 

 This, of course, is probable ; but it must not be 

 forgotten that very slight changes in habits, or the 

 increased uses of other senses than that of smell, 

 may have diminished the value of the information 

 afforded by this gland, and ultimately led to the 

 elimination of the organ itself. It may be that a 

 change from a life habitually passed in forests or 

 scrub to one in open plains would be sufficient to 

 account for such a modification in structure." 



Sir William Flower appears never to have 

 noticed the presence of the slight preorbital de- 

 pression in the skull of certain existing represen- 

 tatives of the horse family ; but when it first came 

 under my own observation the suggestion naturally 

 arose that it was the last vestige of the decadent 

 fore-gland of the three-toed hipparion. 



Confirmation of this was afforded by a statement 

 made by Professor T. H. Huxley,^ that traces of 

 a preorbital pit remain in the skulls of some of the 

 fossil horses from the Siwalik Hills of Northern 

 India. But this was not all, for some years ago 

 I received a communication from a correspondent 

 to the effect that he had seen a living horse, 

 believed to be of Argentine origin, in which there 

 was a distinct depression, although without any 

 external orifice, just in front of each orbit. More 



* Quart. Journ. Geol. Soc, London, vol. xxvi. p. 2, 1870. 



