Disregarding this, some believe that the skull may have belonged to a true ape. If we should imagine the skull of Hylobates agilis to have somewhat more than doubled its mass, we should have a skull of a similar great ape. But if in actual fact a Hylobates had reached such a size, it is quite certain that his cranial capacity would not have increased in the same degree, for we continually find in the most diverse families that large animals have relatively smaller brains than smaller allied species. For example, the dwarf antelope (nanotragus pygmæus) has in proportion to its bodily weight more than four times as much brain as the Beisa antelope.[1] The smaller lower apes very much surpass in this respect the large anthropoid apes, and the gibbons possess, in proportion to their bodily weight, at least twice as much brain as the great anthropoids.[2]
Such an imaginary gigantic Hylobates would be about as tall as a man and about as heavy as the great anthropoids. Its cranial capacity would therefore not exceed some 500 c. cm. But this is only a little more than that of Pithecanthropus. A true ape with a capacity of 900 c. cm., must, on the contrary, be a giant besides which the largest gorillas would be dwarfs. Even if the bodily size increased only in
- ↑ According to Max Weber, Waarnemingen over het hersengewicht van zoogdiernen. Bijdragen tot de Dierkunde, Amsterdam, 1888, p. 14.
- ↑ Compare the statements of Owen, Comparative Anatomy, Vol. III, p. 143, and M. Weber, Zool. Ergebnisse einer Reise in Niederländisch Ost-Indien, pp. 99, 100.
cavity of the skullcap so that I could compare the dimensions of the cranial cavities, two other methods were also used by me, as follows:
A. (1) The external volume of a skullcap above a plane passed symmetrically through the glabella and the external occipital protuberance was determined. (2) Its surface was found by weighing a tin-foil covering that had been spread over it. (3) Its internal capacity was approximately determined by deducting from the value found under (1) the product of the surface found under (2) with the medium thickness of the skull plus the volume of the frontal sinuses. From the result thus obtained (540 c. cm.) the capacity of the entire Pithecanthropus skull was established by (4) comparing with it skulls of Hylobates of as similar build as possible, whose skullcap capacity and total cranial capacity has been determined by direct measurement.
B. After the siliceous matter had been for the most part removed from the skullcap, this was also directly measured by filling it up to the above-mentioned plane with mustard seed and adding to this volume the estimated volume of the siliceous matter yet remaining. I found that the above-mentioned portion of the cavity of the skullcap measured about 550 c. cm. The cast of the cavity of the Neanderthal skull taken to the same plane measures 750 c. cm.
It is well known that Huxley estimated the entire capacity of the Neanderthal skull at 1,236 c. cm. The ratio of the capacity of the skullcap to that of the entire skull is, therefore, 3:5. In a skull of the Hylobates agilis, which, though only half the size, strikingly resembles that of Pithecanthropus, I find the same ratio.
According to all these methods, the total cranial capacity of the Pithecanthropus skull is found to be 900 c. cm., or somewhat more. The difference between this and my earlier estimates (compare also the Verhandl. der Berliner Gesellschaft für Anthropologie, 1895, p. 728) depends upon this, that in the first I did not allow sufficiently for the thickness of the skull (it is about 6 mm.), and secondly I could not directly compare the cavity of the skullcap.
