4 The Bird 
cession of low islands which marked the position of the 
present Rocky Mountains. In the shallow tropical sea, 
extending from this land five hundred miles or more to 
the eastward, and to unknown limits north and south, 
there was the greatest abundance and variety of fishes, 
and these doubtless constituted the main food of the 
present species. Hesperornis, as we have seen, was an 
admirable diver; while the long neck, with its capabilities 
of rapid flexure, and the long slender jaws armed with 
sharp recurved teeth, formed together a perfect instru- 
ment for the capture and retention of the most agile fish. 
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, so the power of swallowing was doubt- 
less equal to almost any emergency.”’ 
Hesperornis had numerous teeth set in grooves like 
those of serpents and crocodiles, but in Ichthyornis (‘Fish- 
bird,’ so called because its vertebre are biconcave like 
those of a fish) the teeth were in separate sockets as in 
alligators. The latter bird was not large, being about 
the size of a pigeon, and it had well-developed wings. 
It is interesting to compare Hesperornis with the 
group of penguins, both being highly specialized, although 
in ways so different, for an almost wholly aquatic life. 
Hesperornis swam by strong strokes of its great webbed, 
or lobed, toes, its wings dangling uselessly for genera- 
tion after generation, until all trace, save a vestigial 
humerus, of their bony support disappeared. Penguins, 
however, make but little use of their feet in swimming, 
only occasionally aiding the tail in steering; but they 
