246 COPE. (VoL. III. 
posterior. In the species of Mioclanus the relation of the 
cusps to the plane may be seen in various stages of transition. 
In most of them the first inferior true molar retains more or 
less of its elevation, which is due to the fact that the first pre- 
molar is always tritubercular, and leaves a triangular space be- 
tween it and the first true molar. 
Figure 69.— Diagrams showing successive modifications of dentition from the 
haplodont (7) to the protodont (2), the triconodont (3), the double tritubercular (4), 
the carnivorous tritubercular (5), to the less and more completed quadritubercular 
(6,7); from Osborn. The genera represented are: 7, Delphinus; 2, Dromothe- 
rium; 3, Triconodon; 4, Peralestes and Spalacotherium; 5, Didymictis; 6, Mio- 
clenus; 7, Hyopsodus. 
The mechanical cause of this change is to be found in the 
relations existing between the opposing molars after the appear- 
ance of the hypocone (fourth tubercle) of the superior series. 
The effect of the latter when it should impinge on the para- 
conid of the inferior molar, 
would be to prevent con- 
tact of the heel (hypoco- 
nid) of the lower molar 
with the interior part (pro- 
tocone) of the superior mo- 
Figure 70. — Relation of the quadritu- lar next posterior to it. The 
bercular superior to the quinquetubercular presence of such a slight 
amferior EHS in mastication; from Osborn, eap would not interfere with 
American Naturalist, December, 1880. Pr. F 
the cracking of seeds or 
protocone; 7%. protoconid; #y. hypocone; 
hy, hypoconid; fa. paracone; fat. para- nuts, but would prevent the 
conid; me. metacone;y me’. metaconid; finer mastication of all sub- 
en?, entoconid; m/. metaconule; //. para- stances. It is pretty clear 
that the mastication would 
have to be performed by the anterior part of the inferior molar 
on the posterior part of the superior, by a dentition passing from 
the tritubercular to the quadritubercular condition. Such use as 
conule. 
