The striking anatomical differences between apes and men, though not of sufficient importance to exclude the possibility of collateral relationship, are so many solid arguments against the theory of direct descent. We will content ourselves with a mere enumeration of these differences. In the ape, the cranium has a protruding muzzle and powerful jaws equipped with projecting canine teeth, but the brain-case is comparatively small; in man, on the contrary, the facial development is insignificant and the teeth are small and vertical, while the brain-case is enormous in size, having at least twice the capacity of that of an ape. “The face of man,” to quote Ranke, “slides, as it were, down from the forehead and appears as an appendix to the front half of the skull. But the gorilla’s face, on the contrary, protrudes from the skull, which in turn slides almost entirely backward from the face. By a cross-cut one may sever the whole face from the skull, except a very small part near the sockets, without being forced to open up the interior of the skull. It is only on account of its protruding, strongly developed lower parts that the skull-cap of the animal can simulate a kind of human face.” (“Der Mensch,” vol. II, p. 401.) These differences may be summarized by saying that the head of the ape is specialized for mastication and defense, whereas the head of man is specialized for psychic functions. Again, as we have seen, the fore-limbs of the ape are long, and its hind-limbs short, the extremities of both the latter and the former being specialized primarily for prehension and only secondarily for progression. This is due to the ape’s adaptation to arboreal life. In man, however, the arms are short and specialized for prehension alone, while the legs are long and terminate in broad plantigrade feet specialized for progression alone. Man, consequently, is not adapted to arboreal life. In the ape, the spine has a single curve, and the occipital foramen (the aperture through which the spinal cord enters the brain-case) is eccentrically located in the floor of the cranial box; in man, the spine has a double curve, and the occipital foramen is centrally located, both features being in adaptation to the upright posture peculiar to man—“_die zentralle Lage dieser Oeffnung_,” says Ranke alluding to the occipital foramen of man, “_in der Schädelbasis ist für den Menschenschädel im Unterschied gegen den Tierschädel eine in hohem Masse typische_.” (“Der Mensch,” vol. I, p. 378.) In the ape, therefore, the vertebræ have an adaptation producing convexity of the back, precluding a normal upright posture, and enforcing progression on all fours. It has, moreover, powerful muscles at the back of the neck to carry the head in the horizontal position necessitated by this mode of progression. In man “the skull has the occipital condyles placed within the middle fifth, in adaptation to the vertical position