The peculiarities of the skull of the Prjevalsky horse (Equus prjevalskii) have been extensively studied by Salensky of St Petersburg, and compared by him with the skulls of various other members of the genus Equus. No special attempt, however, has been made to contrast the skull of the wild horse with that of different varieties of the domestic horse. There can be little doubt that given as rich a collection of Prjevalsky horse skulls as were at the disposal of Salensky, and given, at the same time, a representative collection of skulls of different types of the domestic horse, many points of great scientific interest would emerge from a comparison. In default of such a wealth of material, it is clearly desirable that opportunities afforded by even isolated specimens should be turned to as good an account as possible.