20 THE HORSE AND ITS RELATIVES 



from the forehead downwards to the horizontal 

 bar known as the temporal arch. Secondly, it is 

 characterised by the inordinate length of the por- 

 tion in front of the socket of the eye, or orbit, as 

 compared with the part behind the same. "In the 

 horse," writes Professor H, F. Osborn,^ "lone- 

 headedness is a very ancient character ; even the 

 earliest known four-toed horses have quite elongate, 

 or at least mesaticephalic [moderately long] skulls. 



Skull of a giant extinct Pig-like animal [Elotherititn), to show 

 the horse-like elongation of the facial portion. 



The progressive elongation of the skull in horses 

 is apparently for two purposes : first, to facilitate 

 reaching the ground with the row of incisor or 

 cropping teeth ; second, and no less important, to 

 allow space in front of the eye-sockets for the great 

 rows of elongate, or hypsodont, grinding teeth, the 

 marvellous dental battery of the horse. We might 

 assume from these facts that long-headedness is 

 correlated with long teeth, but the giant pigs 



* The Age of Mammals, New York, 1910, p. 18. 



