SOME EARLY MAMMALS 
247 
j conceive that the earliest ancestors of the horse, finding (perhaps 
'I ^ ^ 
j for the first time in the world’s history) boundless grassy plains 
j before them, were impelled by a strong desire to run ? 
I It is a well-known fact that young horses are occasionally born 
with small extra toes on their feet. Suetonius^ has given an 
account of the famous steed of Julius Csesar. According to the 
I 
j historian, Csesar “ used to ride a remarkable horse, which had feet 
! that were almost human, the hoofs being cleft like toes.” This 
j 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 Coesans, Ixvi. 
