MODERN HORSES AND THEIR ANCESTORS 87 



" Shire " horse (which is derived from the old English war- 

 horse, in the making of which certainly four hundred 

 years ago Arab blood and heavy Northern stock were 

 mingled), do show, as a rule, a well-marked if shallow, 

 cup-like depression in front of the orbit ! In fact, as 

 Mr. Lydekker has pointed out, the presence of this " pre- 

 orbital cup " is evidence of the descent of its possessor 

 from Arab ancestry. Many specimens of horses' skulls 

 showing this "cup" are exhibited in the Natural History 

 Museum. We have not been able to find any trace 

 of a gland like the " larmier " of deer and the " cru- 

 men " of antelopes on examining the soft tissues which 

 overlie this cavity in horses of Arab descent, but it is 

 not improbable that occasional instances of such survival 

 will some day come to light. A very interesting fact in 

 connection with this concavity and its indication of a 

 distinction between the Northern (Mongolian) and the 

 Southern (Arabian) horse is that in India a fossil horse 

 of very late Tertiary date has been found, a true one- 

 toed horse, not a Hipparion, which has the pre-orbital 

 cup well marked, and is possibly the ancestor of the Arab. 



There is no very great difference between the wild 

 horse and wild asses and zebras. They are distinct 

 " species," but will breed together and produce " mules," 

 which in rare cases appear to be themselves fertile, 

 although this is doubtful. The inner causes of the 

 infertility of mules are not really known or understood. 

 Nor, in fact, do we know really and experimentally what 

 are the causes of fecundity and of infecundity in normally 

 paired animals, including mankind. It is of the utmost 

 importance to modern Statecraft that this subject should 

 be studied, and there is a great field for experimental 

 inquiry. 



A clear mark of difference between the horse and the 

 other species of the genus Equus (namely, the Asiatic 



