There is no evidence, however, that these hollow bones were filled with air from the lungs, as in the case of the bones of birds.

The foot is bird-like; the hand is still more so; in fact, no dinosaur hand has ever before been found which so closely mimics that of a bird in the great elongation of the first or index-finger, in the abbreviation of the thumb and middle finger, and in the reduction of the ring-finger.
These fingers, with sharp claws, were not strong enough for climbing, and the only special fitness we have been able to imagine is that they were used for the grasping of a light and agile prey (see figs.

17, 18.) Another reason for the venture of designating this animal as the "bird-catcher" is that the Jurassic birds (not thus far discovered in America, but known from the _Archaeopteryx_ of Germany) were not so active or such strong fliers as existing birds; in fact, they were not unlike the little dinosaur itself.

They were toothed, long-tailed, short-armed, the body was feathered instead of scaled; they rose slowly from the ground.

This renders it probable that they were the prey of the smaller pneumatic-built dinosaurs such as the present animal.
This hypothetical bird-catcher seems to have been designed to spring upon a delicately built prey, the structure being the very antipode of that of the large carnivorous dinosaurs.