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The Evolution of the Horse. 
membrane. In veterinary surgery it is called the " false 
nostril." 
If this were all we knew about this organ, it would be un- 
satisfactory enough ; but it immediately acquires interest when 
we know that in the tapir a similar structure, only in a very 
much more developed condition, is found. In that animal it 
runs upwards, as a long, narrow tube, from the external nostril, 
at first in contact with its fellow of the opposite side, and after- 
wards, taking a curiously-curved course, terminates in a dilated, 
closed extremity, which lies in a distinct groove by the side of 
the upper part of the nasal bone. Its walls are cartilaginous, 
and convoluted in such a manner as greatly to increase the area 
of the internal surface. It is obvious that the " false nostril " of 
the horse cannot be looked upon as anything specially belonging 
to the economy of that animal, but as a rudimentary condition, 
or survival of some structure which is far more highly developed 
in some of the more primitive forms of Perissodactyles. This 
view is greatly strengthened by the recent discovery of an 
exactly similar structure in the rhinoceros, only in a condition 
intermediate between that in which it is found in the horse and 
the tapir. 
Thus, an organ which, when only known in one animal, 
appeared strange, anomalous, and puzzling, because there 
seemed nothing to account for its presence, acquires in the 
light of wider knowledge a much deeper interest ; for, if we 
cannot even yet discover its purpose, its presence in some 
modification in all of these three now very distinct forms, and 
in, as far as is known, no other mammals, is a strong corrobo- 
ration of the view, formed upon other evidence, of their close 
affinity and common descent. 
Other equally mysterious structures are the " guttural 
pouches," also diverticula of the respiratory passages, large 
cavities, one on each side, situated at the base of the skull, 
behind the pharynx, and connected with the Eustachian tubes, 
and which, in the most approved works on veterinary anatomy, 
are said to be " found only in Solipeds." Exactly similar pouches 
exist in the tapir, but I am not aware whether they have as yet 
been looked for in the rhinoceros. 
The next parts to which attention may be called are the teeth, 
which in the horse, though founded upon the same general 
typo as the primitive Ungulates of the Eocene period, have 
undergone a remarkable amount of specialisation, which fits 
them in an eminent degree for the purpose they have to fulfil. 
For convenience of description, teeth are divided, according 
to their situation in the mouth and other characters, into four 
