But the situation is more hopeful, if we hark back to a still more remote period, whose remains are so scarce and fragmentary, as to eliminate the possibility of embarrassment arising from intractable details. “Back of this,” says Osborn, “ ... was a prehuman arboreal stage.” (_Loc. cit._) Here, then, we are back again in the same old rut of tree-climbing simian ancestry, whence we thought to have escaped by abandoning the theory of lineal descent; and, before we have time to speculate upon how we got there, Prof. Wm. Gregory of the American Museum is summoned by Osborn to present us with specimens of this prehuman arboreal stage. This expert, it would seem, favored up till the year 1923 the fossil jaw of the _Propliopithecus_ as representing the common root, whence the human race diverged, on one side, and the races of anthropoid apes, on the other. (Cf. Osborn’s _Museum-leaflet_ of 1923 on “The Hall of the Age of Man,” p. 29.) On April 14, 1923, however, Gregory announced the deposition of _Propliopithecus_ and the enthronement of the jaw of _Dryopithecus_. This sudden accession of _Dryopithecus_ to the post of common ancestor of apes and men was due to the discovery by Dr. Barnum Brown of three fossil jaws of _Dryopithecus_ in the Miocene deposits of the Siwalik beds in northern India. By some rapturous coincidence, the three jaws in question happen to come from three successive “horizons,” and to be representative of just three different stages in the evolution of _Dryopithecus_. Doctor Gregory finds, moreover, that the patterns of the minute cracks and furrows on the surviving molar teeth correspond to those on the surface of the enamels of modern ape and human teeth. Hence, with that ephemeral infallibility, which is characteristic of authorities like Doctor Gregory, and which is proof against all discouragement by reason of past blunders, the one who told us but a year ago that the cusps of all the teeth of _Propliopithecus_ “are exactly such as would be expected in the common starting point for the divergent lines leading to the gibbons, to the higher apes, and to man” (_loc. cit._), now tells us that both we and the apes have inherited our teeth from _Dryopithecus_, who had heretofore remained neglected on the side-lines. In 1923, apparently, Dr. Gregory was unimpressed with the crown patterns of _Dryopithecus_, whose jaw he then excluded from the direct human line. (Cf. _Museum-leaflet_, p. 5.) Now, however, that the new discoveries have brought _Dryopithecus_ into the limelight, and, particularly because these jaws were found in _Miocene_ deposits, Gregory has shifted his favor from _Propliopithecus_ to _Dryopithecus_. (Cf. _Science_, April 25, 1924, suppl. XIII.)