POSITION AND STRUCTURE OF HORSE 51 



no prima facie reason why the chestnuts of the 

 EquidcB should not be decadent glandular structures, 

 the decadence being more marked in those of the 

 horse than in the single pair of the asses and 

 zebras. 



There is, however, another point which may 

 have an important bearing on the subject. As 

 already mentioned, the presence of a depression in 

 the skulls of certain extinct three-toed horses renders 

 it probable that primitive horses were furnished 

 with face-glands comparable to those of deer ; such 

 glands probably having a function somewhat ana- 

 logous to that of the scent-glands on the limbs 

 of the latter. If, then, the existing EquidiB have 

 got rid of their face-glands, as being (perhaps on 

 account of change of habit) useless, it is conceivable 

 that, for the same reason, they may have also 

 discarded their limb-glands. 



And there is some reason to believe that such 

 a change of habit has taken place during the 

 evolution of the family. Mr. R. I. Pocock,^ for 

 instance, in a paper on the primitive colouring of 

 the members of the horse tribe, to which fuller 

 reference is made later, has suggested that the 

 ancestral animals were inhabitants of forests, in- 

 stead of open plains, remarking that this primitive 

 type of colouring "would lend itself especially to 

 concealment in horses accustomed to shelter in 



^ Ann. Mag. Nat. Hist., London, ser. 8, vol. iv. p. 409, 1909. 



