Even small fishes could not possibly have been swallowed by the mosasaurs in any other way than head first, since the backwardly projecting, and often long, spines would have rendered any other procedure impossible. Even after the head had entered the gullet, deglutition could have been effectively completed only by the aid of some mechanism whereby the fish could have been pulled or pushed back into the constricting fauces. The strong teeth of the upper jaws and palate held firmly the struggling prey, while the loosely united jaws, bending laterally at the joint back of the middle, either alternately, or more probably in unison, steadily forced it far enough back to be seized by the muscles of the fauces. The shape of the mosasaurs, though slender, does not suggest extraordinary speed in the water; doubtless most of the fishes that lived in the seas with them could swim faster than they. Their prey was captured, for the most part at least, by sudden and quick lateral movements, for which their powerful and flexible paddles admirably adapted them. It is a rather remarkable fact that, among the thousands of specimens of mosasaurs which have been collected during the past forty years in both Europe and North America, there never has been found one of a very young animal. Of almost all other animals occurring abundantly as fossils some specimens are sure to be discovered of young and even embryonic individuals. It is quite certain that all such voracious monsters as were the mosasaurs did not die of old age. Some specimens, it is true, have been found that were evidently not full grown animals, but the observed differences in the size of the fossil bones are not great. All are of adult or nearly adult animals. If the mosasaurs were oviparous, as were the ichthyosaurs, and probably the plesiosaurs, and as are some living land lizards, the apparently entire absence of embryonic bones associated with often nearly complete skeletons of the mosasaurs is inexplicable; certainly _some_ mosasaurs must have died a short time before the birth of their young. But embryos have never been discovered, though numerous skeletons inclosing fossilized stomach contents have been found. From this fact it would seem very probable that the mosasaurs were oviparous, as are most other lizards. But this, after all, may be a hasty inference.