{250}Besides these external characters, we find, on examining their bony structure, much variation in the skull. Some have a rounded forehead, the ascending portion of the lower jaw being high, broad, and flat, with a large facial angle; in others, we have great production of the upper jaw (the horizontal part of the lower jaw being greater than the ascending portion), and a low facial angle. The cerebral portion of the skull is long and flattened, and the palate long and narrow. The dental formula is I2/2, C1/1, P2/2, M3/3 = 32, that of the milk-teeth I2/2, C1/1, M (the forerunners of the permanent _pre-molars_) 2/2 = 20, exactly the same as in a Man. The outer lower incisors are equal to, or sometimes smaller than, the inner pair. The permanent canines--which are long and sharp--come in before, or with the posterior molars of both jaws. Between them and the incisors above, and between the canine and the anterior pre-molar below, occurs a gap (or diastema). The anterior upper pre-molar has its outer cusp modified and sharpened; the anterior lower pre-molar has the anterior margin of its crown so shaped as to work "as a scissors'-blade against the posterior edge of the upper canines." (_Henley._) The crowns of the molar teeth are long from before backwards, and their fore and hind cusps are united by transverse ridges, a third being present in the same genera, on the posterior lower five-cusped molar. The nasal bones are often ossified together to form one bone. The surface of the skull is in general oval and smooth, but in some of the Baboons there appear strong ridges over the eyes (hiding the forehead) and along the top of the head, being stronger, when present, in the male than in the female. The external orifice to the ear has a considerable bony tube, or meatus, a distinguishing character which is absent in the New {251}World Monkeys; their tympanic (or ear) cavity being close to the outer wall of the skull. The line of junction (or suture) between the upper jaw-bones, the pre-maxillary and the maxillary, remains unclosed until long after the permanent teeth have come in. Sometimes it remains unclosed throughout life. The foramen for the passage of the spinal-cord, and the condyles for the articulation of the skull with the neck, lie far back. In the spinal column there are nineteen dorsal and lumbar vertebræ together. The number of caudal vertebræ varies greatly; in some there are as many as thirty-one, in others only three. The posterior ends of the ischiatic bones of the pelvis are rough, flattened, and broad, for the attachment of the fleshy callosities mentioned above. The bones of the thigh and leg (_femur_ and _tibia_) together, are longer than those of the arm and fore-arm (_humerus_ and _radius_) together. The bones of the thumb are modified more for support and progression than for the actions of a true hand; by these modifications the movements of rotation (pronation and supination) are much restricted.