SOME EARLY MAMMALS 247 



conceive that the earliest ancestors of the horse, finding (perhaps 

 for the first time in the world's history) boundless grassy plains 

 before them, were impelled by a strong desire to run ? 



It is a well-known fact that young horses are occasionally born 

 with small extra toes on their feet. Suetonius 1 has given an 

 account of the famous steed of Julius Csesar. According to the 

 historian, Ctesar " used to ride a remarkable horse, which had feet 

 that were almost human, the hoofs being cleft like toes." This 

 account clearly indicates the presence of extra digits, and the 

 occurrence is more frequent than is generally supposed. Pro- 

 fessor Marsh has made a study of this subject, since it has an 

 important bearing upon the history of the evolution of the horse 

 as given above ; for in the light of modern teaching such occur- 

 rences are but " reversions " to older types that lived ages ago. 

 He has therefore examined a large number of living animals with 

 this peculiarity, and several interesting specimens of the same 

 character have been sent to him : he has likewise received photo- 

 graphs, drawings, and detailed descriptions of various other 

 examples, the authenticity of which cannot be questioned. The 

 various cases he has come across may be summed up as follows : 



Sometimes there is only one extra digit on one foot. This is 

 always much smaller than the main or third digit, the largest he 

 has seen being about one-half its size, and the smallest very 

 diminutive. This extra toe is almost invariably on the inner side 

 of the main digit, and usually on the fore foot. Sometimes it is 

 entirely hidden beneath the skin, the only external evidence of 

 its presence being a prominence, which, on close examination, may 

 be found to contain, below the " splint-bone," two or more bones 

 corresponding to the finger-joints of our own hands. Sometimes 

 a corresponding extra toe is developed on the other fore foot. At 

 1 De Vita Ccesaris, Ixvi. 



