3 1887] The Perissodactyla. 1071 
inferred from this that Hippotherium is a descendant of some 
genus of Sect. I, a, while Protohippus came from a genus of 
Sect. I, aa, The second point of modification to be ob- 
served in the Hippotheriinz is the enlargement of the 
expansions of the internal extremities of the adjacent 
horns of the crescents of the inferior molars, which is 
Fy iginal; from the 
S 39. Protohippus sej „third natural size. Origi 
we ejunctus Cope, one-thir 5 ¥ 
i Fork Miocene of Colorado. Fig. a, skull, left side; 4 eee = ne 
> Posterior foot, left side; d, ditto, front; e, distal end of metapodials; f, prox 
tnd of Ungual 
l phalange or hoof. 
i ag obvious on wearing, and which are foreshadowed in Anchi- 
a ‘terium (Fig. 35, 4, ai, ai’). The third evidence of progress 1S 
7 “en in the deposit of cement, which fills the valleys of the teeth, 
Tra the two bicipital grooves of the humerus, which nee 
Shp with those seen in the Equide. Fifth, the cupping 9 
towns of the incisors. This only commences W 
> of the cup, as has been shown by Scott. 
