262 Marsh's Monograph on the Odontornithes 
flexure, and the long slender jaws armed with sharp recurved 
teeth formed together a perfect instrument for the capture and 
retention of the most agile fish, As the lower jaws were 
united in front only by cartilage, as in Serpents, and had on 
each side a joint which admitted of some motion, the power of 
swallowing was doubtless equal to any emergency. 
‘Having thus shown what the skeleton of Hesperornis is, 
and what its mode of life must have been, it remains to con- 
sider the more important question of how the peculiar combi- 
nation of general and specialized characters manifested im its — 
structure originated. The two most striking features of Hespe- 
rornis are the teeth, and the limbs, and an inquiry in regard 
to them first suggests itself. 
Figure 3.—Tooth of Hesperornis regalis (No. 1206); enlarged eight diameters. 
Figure 4.—Tooth of Mosasaurus princeps, Marsh; half natural size. a 
a. enamel of crown; b. dentine; b’. root of tooth; c’. absorbed cavity 
root; d. young tooth. 
_ “The teeth of Hesperornis may be regarded as a character 
inherited from a reptilian ancestry. Their strong resemblance 
to the teeth of reptiles, in form, structure, and succession, A 
have in one well known group of reptiles exemplified, by. 
Ichthyosaurus. This method of insertion in the jaw 18 & ge” 
tive dental character, quite different from what we shoulé 
