On the Bengawan River in central Java, a Dutch army surgeon, Eugen Dubois, had been excavating for fossils in the hope of finding prehuman remains. In the year 1891 he found near Trinil a deposit of numerous mammal bones, including a single upper molar tooth which he regarded as that of a new species of ape. On carefully clearing away the rock the top of a skull appeared at about a meter's distance from the tooth. Further excavation at the close of the rainy season brought to light a second molar tooth and a left thigh-bone about 15 meters from the spot where the skull was found, imbedded and fossilized in the same manner. These scattered parts were described by Dubois(13) in 1894 as the type of _Pithecanthropus erectus_,[O] a term signifying the upright-standing ape-man. The specific term _erectus_ refers to the thigh-bone, of which the author observes: "We must therefore conclude that the femur of _Pithecanthropus_ was designed for the same mechanical functions as that of man. The two articulations and the mechanical axis correspond so exactly to the same parts in man that the law of perfect harmony between the form and function of a bone will necessitate the conclusion that this fossil creature had the same upright posture as man and likewise walked on two legs.... From this it necessarily follows that the creature had the free use of the upper extremities--now superfluous for walking--and that these last were no doubt already far advanced in that line of differentiation which developed them in mankind into tools and organs of touch.... From a study of the femur and skull it follows with certainty that this fossil cannot be classified as simian.... And, as with the skull, so also with the femur, the differences that separate _Pithecanthropus_ from man are less than those distinguishing it from the highest anthropoid.... Although far advanced in the course of differentiation, this Pleistocene form had not yet attained to the human type. _Pithecanthropus erectus_ is the transition form between man and the anthropoids which the laws of evolution teach us must have existed. He is the ancestor of man." Thus the author placed _Pithecanthropus_ in a new family, of the order Primates, which he named the Pithecanthropidæ. [Illustration: FIG. 31. Geological section of the volcano of Lawoe in the Solo River basin. Drawn by C. A. Reeds.] [Illustration: FIG. 32. Map of the Solo River, showing the _Pithecanthropus_ discovery site, also two excavations (Pit No. 1, Pit No. 2) in the ancient gravel of the river-bottom, made by the Selenka-Blanckenhorn expedition of 1907. After Selenka and Blanckenhorn.]