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TEETH OF THE VERTEBRATA. 421
the smallest, the outer pair the largest. The canines are large, pointed,
and recurved. The anterior premolars above are two-rooted and have
premolariform crowns. The third and fourth are three-rooted, with
Fig. 203.
Hywnodon horridus, Leidy. Skull, one-half natural size (from Cope, after Leidy).
three external and one internal cusp, which in the third premolar is
small and placed far back ; in the fourth it is large and has a position
nearer the middle of the tooth ; while in the first and second molars it
is anterior and more or less rudimental. The anterior cusp and median
