In all the large apes these “eye” teeth are of great size. Their purpose, it would seem, is primarily to serve as weapons in conflicts between rivals. Such conflicts are apparently unintentionally, and unavoidably, provoked by the loud cries uttered by the males in their endeavours to discover the whereabouts of females desiring mates. Of necessity roaming far in search of food, the unmated have no means of making their whereabouts known, save by thus giving tongue to desire. Evidently the normal methods of voice production do not suffice for their urgent needs, for the carrying power of the voice is immensely fortified by means of great air sacs, or chambers, formed in part by an enlargement of the body of the hyoid, or the bone which supports the tongue, and in part by dilatations of the inner walls of the larynx. The females, it is to be noted, are by no means so well equipped in this matter. It is not necessary that they should be. All that those desiring mates have to do is to follow up the cries of avid males, a by no means difficult task, especially when under the spell of the emotions which possess them. But the mechanism which serves the Chimpanzee and the Gorilla by no means fulfils the needs of the Orang-utan. In this uncouth creature the system of resonating chambers is immensely increased by great, thin-walled, membranous pouches extending round the neck and under the armpits, so that when inflated these areas have a most extraordinarily swollen appearance. When the Orang chooses to lift his voice even the deaf must hear. Where fighting instead of fondling is the sequel to these impassioned cries the conflict is probably not of long duration, for it is certainly severe. This is attested by the fact that captured specimens, if adult, are commonly found to be minus one or more fingers, which have been bitten or torn off in these love affairs. [Illustration: Plate 2. _From a drawing by I. Thornton._ THE GORILLA PREPARING FOR HOSTILITIES. Note the “beetling” brows, the large size of the canine teeth, and the great development of the arms in these arboreal creatures, which play an even more important part in locomotion than the legs. The latter in this illustration are, however, relatively too small. [Face page 42.] An added ferocity of expression is given to the male Gorilla by the development of enormous brow ridges and the huge canines. The former are regarded by some authorities as adaptations to afford increased powers of mastication. But if this were so, then such ridges should be equally developed in both sexes, and this is far from being true. Hideousness, rather than ferocity, has been given to the Orang-utan by the out-growth of enormous ridges on each side of the face, and these, when the great wind-bags encircling the neck are inflated, impart a repulsiveness of expression attained by no other animal living.