No.2.] THE HARD PARTS OF THE MAMMALIA. 249 
two cusps. The result is an inferior quadritubercular molar, 
which opposes the superior molar which chiefly lies above it, 
together with a small posterior part of the superior molar in 
front of the latter. 
It is a fact that the majority of Mammalia with bunodont 
dentition (the peccary, man) are also isognathous, while the 
majority of the lophodont types are anisognathus (tapir, ox). 
Striking exceptions to the latter rule are seen in the Rodentia 
and in the elephant. But there is evidently some connection 
between anisognathism and the lophodont dentition. Examina- 
Figure 73.— Transverse sections through the maxillary apparatus of a, Fiber; 
6, Lepus; ¢, Dicotyles; ad, Cervus; e, Equus. Figs. @ and ¢ represent isognathous 
dentition, and 4, d, and ¢ anisognathous; from Ryder. 
tion shows that the anisognathous lophodonts have a different 
articulation of the lower jaw from that of the isognathous lopho- 
donts. It is also found that the movement of the lower jaw on 
the upper in the bunodonts differs from that which is exhibited 
by either of the lophodont types, and that this motion is in some, 
but not all cases, rendered necessary by the shape of the articu- 
lation of the lower jaw with the skull. The motions of the three 
types may be represented as follows :— 
BUNOGONE 2 i ius'x AS (Orta perme vent... vertical: 
Eophodont,typeone . |. . “(ectallandiental).. . . . transverse. 
Lophodont, type two . . . (propalinal). . . . . . anteroposterior. 
In the bunodont type the movement of the jaws in mastica- 
tion is identical with that belonging to the tritubercular type, 
in which no other than the vertical is possible. It is rendered 
