The teeth afford us important material for comparison. In the case of anthropoids the formula for the teeth of the slender-nosed or Old-World apes (_Catarrhina_) will generally apply: _i_ 2/2 _c_ 1/1 _p_ 2/2 _m_ 3/3. The following is the formula for the milk-teeth: _i_ 2/2 _c_ 1/1 _m_ 2/2. Magitot and Giglioli[76] have shown that the milk-teeth are cut in the same order as those of man--first, the lower; second, the upper incisor teeth; third, the front pre-molars; fourth, the back pre-molars; fifth, the canine teeth. According to the same authors, the permanent teeth are cut in the following order:--first, the first molar teeth; second, the lower, and then the upper incisor teeth; third, the pre-molars; fourth, the canine teeth; fifth, the second molar teeth; sixth, the third molar teeth. In the skull of a male gorilla, Giglioli found that the permanent canine teeth were cut almost simultaneously with the third molar teeth, and after the appearance of the second molar teeth. The cutting of the canine teeth appears to be a longer process than that of the other teeth. In anthropoids the structure of the permanent teeth varies with the species, and even with the sex. In the gorilla the two upper central incisor teeth are wide, chisel-shaped, and much larger than the pair of lateral incisors. The four lower incisor teeth are of about the size of the upper lateral incisors, and, like these, are chisel-shaped, but not so wide. The powerful upper canine teeth of an aged male are curved in their lower part, both outwards and inwards. Their form is that of a three-sided, cuneiform pyramid. The anterior surface is rounded, and near its inner edge a deep furrow may be observed, extending from the neck of the tooth almost to its point. The outer and inner sides of the tooth meet in a sharp angle, somewhat convex in front, and level or slightly concave behind. The inner side is concave, and furnished, nearly in the centre, with a deep longitudinal farrow. The lower canine teeth of an aged male are shorter than the upper, curved on their upper and outer surface, and somewhat behind. Their form is also that of a three-sided pyramid, rounded in front. The longitudinal furrow which traverses their inner segment is much shorter than that on the upper tooth. The outer side is somewhat convex, and at the same time somewhat retreating, and is provided on its posterior segment with two longitudinal furrows, or more rarely with one, reaching from the neck to about the centre of the tooth. The inner side, like that of the upper teeth, is somewhat concave. The lower canine teeth project like pillars over the upper ones (Figs. 15, 16). The canine teeth of a young male gorilla are less sharp in their angles, although they already present the form of a three-sided pyramid. The canine teeth of the adult female gorilla are much smaller than those of the adult male, and are laterally more compressed. The three-sided pyramidal form is only slightly marked.