With the following account of the numerous species of the genera of this family, we come to consider the first section of the Old World, or Catarrhine[14] Monkeys. These are {249}distinguished from their New World cousins, described in the previous pages, by many important and obvious characters. The partition dividing the nostrils is narrow, instead of broad, and the openings of the nostrils themselves are directed downwards and outwards. Certain genera possess also sacs formed by distensible folds of the skin in the cheeks. These "cheek-pouches" serve as a storing-place by the side of the jaws, for food which they cannot masticate at the moment. When this store is disposed of, the folds of skin come together again and give no indication of the presence of the pouch, which, moreover, when full does not interfere with the mastication of other food in the mouth, or with the utterance of the animal's usual cries. The hind-limbs are never shorter than the fore-; they may be equal in length, but they are generally somewhat longer, the animal being more or less quadrupedal, or very partially erect in gait. Their thumb is not invariably present, but when it is, it is always opposable to its fellow digits. The great-toe is never rudimentary, and is never, as it is in Man, the longest, but is the shortest digit of the foot, and it is capable of free motion to and from the others. All of the digits possess nails. The length of the foot among this group approximates more to the proportions of the foot in Man. The hairs on the arms and fore-arms are directed downwards from the shoulder to the wrist. The tail in this family varies very much; it may be long or short, or even externally absent, but it is never prehensile. All the species, however, possess "callosities," or hard fleshy pads--often of large size--on the buttocks or seat, which, like the naked skin of the face, are usually brilliantly coloured and often of large size. The perineal region and organs are at certain periods, especially in the females, subject to great turgescence and brilliant coloration.