Wallace declares that a large area of unbroken and tolerably high primeval forest is necessary for the well-being of the orang. Such forests are like open ground to them, since they can move to and fro in every direction, with the same ease that the Indians cross the prairie and the Arabs the desert; they go from the top of one tree to the other without ever touching the ground. Those tracts of country which stand high and dry, being more frequented by men, and more often traversed by clearings, and subsequently covered with a low-growing jungle, are unsuitable to the motions characteristic of this animal. He is, in these tracts, more exposed to danger, and more frequently constrained to descend upon the ground. It is also probable that in the district frequented by orangs there is a greater variety of fruits, since the low hills, which stand like islands in the marshy plain, serve as gardens or plantations in which the trees of the hill country flourish. Wallace observes that it is strange and interesting to watch an orang passing at his ease through the forest. He goes with circumspection along one of the larger branches in a half-upright position, which is rendered necessary by the great length of his arms and the shortness of his legs. He seems always to choose such trees as have their branches interwoven with those which surround them, and when these are within reach he extends his long arms, seizes the boughs in question with both hands, as if to try their strength, then swings himself carefully on to the next branch, and goes on as before. The woodcut we subjoin, taken from a photograph by Hermes, in the Berlin Aquarium, may help to explain this ape’s mode of climbing[115] (Fig. 63). [Illustration: Fig. 63.--Climbing orang-utan, seen from behind.]