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the attachment of horns. The limbs were intermediate in 
proportions between those of the elephant and rhinoceros ; but, 
as in the latter, the femur has a third trochanter, and a deep 
pit for the round ligament. The feet were short and stout, 
but in essential characters agree with the true Perissodactyles, 
and have four toes in front and three behind. 
Numerous species have been described, both by Cope and 
Marsh, founded chiefly upon the form and direction of the 
horn cores on the nasal bones : they are all from the Miocene 
beds east of the Eocky Mountains, in Dakota, Nebraska, Wyom- 
ing, and Colorado ; and there is no evidence of any of the 
Titanotheridce , as the family should be called, after the first- 
characterised genus of the group, having survived to a later 
geological epoch. 
Fig. l. 
“ 1 c 3 e 
Diagram of several stages of modification of the feet of extinct forms of American 
horse-like animals (chiefly from Marsh), showing gradual reduction of the } 
outer, and enlargement of the middle toe (III). 
a, Orohippus (Eocene) ; b, Mesohippus (Miocene) ; c, Miohippus (Miocene) ; 
d, Hipparion or Protohipp'us (Pliocene) ; e, Equus (Pleistocene). 
When we pass to the Pliocene and Pleistocene times, the 
Perissodactyles met with can all be referred to one or other of 
the three existing families ; all the intermediate forms, and all 
those which have attained a different type of specialisation, as 
those last named, have completely disappeared. 
Eemains of several species of Bhinocerotidce were very 
abundant during the Pliocene period in western North America; 
they all appear to belong to the hornless type, and from causes 
unknown became entirely extinct before the Pleistocene age. 
No rhinoceros exists now on the American continent, nor is 
there evidence that it ever supported animals belonging to the 
minor groups of the family to which the existing Indian, 
Sumatran, or African rhinoceros pertain. 
