1070 The Perissodactyla. [Dec, 
The phylogeny of the genera of this family is clearly, then, 
as follows: The genera with distinct internal tubercles must be 
tr. go me. regarded as primitive (Sect. I, a), 
cate and those with completed crests 
(I, aa) are derivative forms. The 
Hippotheriinz are still later de- 
scendants on various accounts. 
First, the development of the 
intermediate tubercles is much 
greater than in any other genera. 
These tubercles are somewhat 
enlarged in Anchitherium (see — 
Fig. 35, the anterior one), and — 
they extend much further antero- 
posteriorly in Anchippus. In 
the Hippotheriine they reach 
and join each other at the mid- 
dle of the crown (Fig. 40). In 
this transition the relations of 
Fic. 37. Hanes, the  intériar tubercles are = ‘ 
, ae ioe ve pdam ef mete rious; for in Hippotherium, “o 
thd Migcbue of Sanan Panes: Fig. of them (the anterior), rena : 
, from Monts Z, from right side. distinct, while in Protohippus 
(Fig. 39) both are confluent with the intermediates. It may’ 4 
Berea 
= 
% Fic. 38. Hippotherium speciosum Lei 
__ braska, se natural size. Original 
: k bed of Nè 
dy, skull, from the Loup Ae sides 6 W0 
T Superior molar teeth from helow. ; ai 
Fig. a, from below; b, 
