In brain development the anthropoids are, as already mentioned, greatly inferior to man; in the Gorilla, the largest-brained type, the cranial capacity never, so far as is known, exceeds 600 cubic centimetres, whereas the average in man is about 1500, and the smallest known about 930. Apart from the difference in size, however, there is a surprisingly close similarity between the anthropoid and the human brains, which may be followed even in the particular arrangement of the fissures. That the gap between the two types in respect of the character in question is by no means extraordinarily wide may be seen from Fig. 137, in which a series of brains are depicted. The size of the hemispheres and the wrinkling of their surface are the characters from which we judge the brain development, and it is obvious that in these respects the step from the lower monkeys to the Chimpanzee is greater than that between the Chimpanzee and the lowest human type. In the teeth also, as is shown on Fig. 138, there is a gradual change from the lemur to the human type. [Illustration: FIG. 138. _A_, Lower jaw of Pelycodus, a primitive extinct lemur, with eleven teeth on either side; _B_, Lower jaw of red howling monkey (a Western ape), with nine teeth on either side; _C_, Lower jaw of chimpanzee, with eight teeth on either side; _D_, Lower jaw of man.] [Illustration: FIG. 139.--The Pithecanthropus skull from the side and from above.] [Illustration: FIG. 140.--The Pithecanthropus femur, from behind. The bone shows an exostosis, evidently caused by an injury.] Thus there can be no reasonable doubt that man has evolved from an ancestor which, if it existed to-day, we should without hesitation class as an anthropoid ape. Could any doubt have remained, it would have been set aside by the discovery, in 1891, of a being occupying a position about midway between the highest apes and the most primitive known man. This is the Pithecanthropus, whose remains were discovered in Java in a volcanic deposit of somewhat doubtful age, but probably belonging to an era when a primitive type of man was already in existence. The remains were indeed somewhat scanty, consisting of the roof of the skull, a thigh bone, and a fragment of the lower jaw, the former two of which are illustrated in Figs. 139 and 140. From these fragments of the skeleton numerous deductions have been drawn, of greater or less probability. It may be said with practical certainty, however, that this ape-man was of the size of a smallish man, and that he was accustomed to walk and stand in the characteristically human erect attitude. The cranial capacity has been calculated at from 850 to 1000 cubic centimetres, or considerably greater than the highest existing apes, and about equal to that of the lowest known human specimens. His statue, as his discoverer conceived him, is illustrated in Fig. 141. [Illustration: FIG. 141.--Imaginative statue of _Pithecanthropus erectus_.]