1902-3.] The Wild Horse (Equus prjevalskii). 
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horses I have seen the heels (points of the hocks) almost touch 
•each other, as in many Clydesdales, and the hocks are distinctly 
bent. In the hybrid the hocks are as straight as in well-bred 
foals, and the heels are kept well apart in walking. 
Another difference of considerable importance is, that while 
the wild horse neighs, the hybrid makes a peculiar barking sound 
remotely suggestive of the rasping call of the Kiang. 
The dun Mongol pony’s hybrid arrived five weeks before its 
lime, and, though perfect in every way, was short-lived. Only in 
one respect did this hybrid differ from the one already described. 
In the Exmoor hybrid the hock callosities are entirely absent ; in 
the Mongol hybrid the right hock callosity is completely wanting, 
hut the left one is represented by a small, slightly hardened patch 
of skin sparsely covered with short white hair. 1 In zebra hybrids 
out of cross-bred mares the hock callosities are usually fairly large, 
while in hybrids out of well-bred pony mares the hock callosities 
are invariably absent. The Exmoor pony, though not as pure 
as the Hebridean and other ponies without callosities, has un- 
doubtedly a strong dash of true pony blood ; the Mongol pony 
is as certainly saturated with what, for want of a better term, may 
be called cart-horse blood. As I expected, there were no hock 
callosities present in the Exmoor hybrid. In the Mongol hybrid 
there was less evidence of hock callosities than I expected. 
From what has been said it follows that a Kiang-Mongol-pony 
hybrid differs from Prjevalsky’s horse (1) in having the merest 
vestiges of hock callosities ; (2) in not neighing like a horse ; (3) in 
having finer limbs and joints and less specialised hoofs ; (4) in the 
form of the head, in the lips, muzzle, and ears • (5) in the dorsal 
band ; and (6) in the absence even at birth of any suggestion 
of shoulder-stripes and of bars on the legs. 
While most of the zoologists who hesitated to regard Prjevalsky’s 
horse as representing a distinct and primitive type favoured the 
view that it was a mule, some asserted that it in no way essentially 
differed from an ordinary horse. The colts brought from Central 
Asia, they said, were the offspring of escaped Mongol ponies. 
1 The presence of hair in the imperfectly-formed hock callosity of the Mongol 
hybrid, together with the presence of hair rudiments in the developing hock 
•callosity of the common horse, certainly lends very little support to the view 
held by some zoologists that the chestnuts of the horse are vestiges of glands. 
