ANCIENT AND MODERN HIPPOPOTAMUSES 263 
of the head, and especially the great width of the mouth, 
the prominent position of the eyes and nostrils, the minute 
ears, bulky body, short and stout limbs, and short tail, 
are among the most striking external features of the 
creature. The presence of hoofs (four in number on each 
foot) shows that the hippopotamus belongs to the great 
order of hoofed, or ungulate, mammals, and the thickness 
of its nearly naked hide led the older naturalists to place 
it among what used to be called the pachyderms. It has 
been shown, however, by anatomical investigations that the 
group thus designated, which included such totally different 
forms as elephants, rhinoceroses, and hippopotamuses, is 
an entirely artificial one, and that the last-named animals, 
together with their near relatives the pigs, are much more 
closely connected with the ruminants. 
If the reader desires to know why zoologists place such 
very dissimilar-looking animals as the hippopotamus and 
the giraffe in the same great group, while they sunder 
from the former the apparently more similar rhinoceroses, 
it may be replied that this is largely due to the difference 
in the structure of the feet of the two groups. In that 
the bones of the skeleton of the two middle toes are 
symmetrical to a line drawn between them, the hippo- 
potamuses and pigs resemble the ruminants, whereas the 
rhinoceroses agree with horses in having the middle toe 
(which is alone present in the latter) symmetrical in itself. 
One of the essential characteristics of the ruminants is 
the circumstance that in the lower part of the leg the 
two middle toes are supported by a single bone known 
as the cannon-bone, which consists anatomically of two 
originally distinct elements welded together, while the 
supporting bones of the small lateral toes are incompletely 
developed. If, on the other hand, we examine the skeleton 
