In the human jaw A we see behind the narrow front border _a_ the large semicircular excavations for the attachment of the digastric muscles right and left. They pass from here to the hyoid bone. From the spine (double in origin) between the two digastric impressions passes a pair of muscular slips, called the genio-hyoid muscles, also to the hyoid bone, and from the pair of spines marked _y_ a pair of muscles, called the genio-glossals, pass to the tongue. These inferior and superior mental spines and the digastric impressions, much smaller in size than in man, are seen in the chimpanzee's jaw, C, but are rubbed or partly broken and partly rubbed away in the Piltdown half-jaw, B. In the figures A and C the size of the digastric impressions and mental spines is exaggerated, but their relatively much greater size in man than in the chimpanzee is correctly given, and this greater size is connected with the greater control of the tongue and the floor of the mouth in man, possibly connected with speech.
_Reference Letters._--a, Broad, upwardly and forwardly sloping surface, reduced in man; b, lower border of the jaw-bone; x, front margin of the digastric "impression" of the right side. Dig, digastric impression; y, superior mental spine of the left side; Fr., fractured edge of the Piltdown jaw, and corresponding region in that of the chimpanzee.]
So long as the Neanderman was the sole indication of a creature nearer in some features to the apes than are any living or extinct races of the species Homo sapiens, the view was possible that the two stocks which to-day blossom and display themselves--the one as the human race, the other as the man-like apes (gorilla, chimpanzee, orang, and gibbons), became separated from one another in long past geologic ages, and that they have undergone each an independent development from a creature so unlike both as seen to-day, that we cannot speak of it as a missing link or a link at all. That view must be considerably modified by the discovery of the Piltdown jaw--the jaw of Eoanthropus Dawsoni--which is not that of a "man," that is not of the genus Homo, but must, in my judgment, be considered as one of the family Hominidæ--a Hominid, as we may say--a species assigned to a new genus Eoanthropus by Smith Woodward, which is grouped with the genus Homo and the ill-defined genus Pithecanthropus, to form the family Hominidæ; just as the genera Gorilla, Anthropopithecus (chimpanzee), Simia (orang), and Hylobates (gibbon) are grouped together to form the family Simiidæ. In Eoanthropus we have in our hands, at last, the much-talked-of "missing link"--the link obviously connecting man, the genus Homo, with the apes.