Page:Popular Science Monthly Volume 41.djvu/403

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HE slender and the short-thumbed monkeys belong, in the truest sense of the word, to an old simian family. The fact is demonstrated as to the Indian slender monkeys, for indubitable representatives of this genus (the Semnopithecus) lived in the Tertiary period.

The form of the skull gives the slender and short-thumbed monkeys a peculiar appearance. It is roundish, the snout advancing but little in front of the forehead, and the bony crests and edges, which often give the skull of the male an appearance like that of a beast of prey, are hardly distinguishable. In a corresponding way the jaw is relatively only slightly projecting, and less obvious in the slender than in the short-thumbed monkeys. The entire skeleton in both groups is distinguished by the slenderness and lightness of its form, from which the slender monkeys get their name. The name of the African short-thumbed monkeys relates to a peculiarity of their bony structure, in that the thumbs of their fore limbs are not visible externally except as stumps; and, while in the slender monkeys, too, the thumb is behind the other fingers in development, the complete arrest of it in the others has been held sufficient to mark a distinction between the two families. On the other hand, I find a peculiarity of the skeleton of the slender monkeys mentioned in only a few descriptions, and in those casually, which appears to me as doubly striking in the monkeys as climbing animals, and is not elsewhere repeated in them, at least in those of the Old World. It is that the slender monkeys have much longer and thicker hind legs than fore legs; the development of the hind limbs evidently surpasses that of the fore limbs; and this occasions characteristic deviations in the attitudes and movements of the animals, as I have observed daily with my pets. The slender monkeys run half erect with their hind legs bent up, and make great leaps from this position direct. Thus, notwithstanding their great agility, they have something hasty and angular in their motions, and maintain so peculiar a gait that any one who has studied them continuously in living specimens can distinguish at a glance whether a picture of them is made from life, or whether it has been constructed by adding a few special outward marks of the slender monkey to the figure of a common monkey. In their inner structure the slender monkeys and the short-thumbed monkeys have a highly important peculiarity, unique in its way, in the shape of a composite, divided stomach, suggestive of the ruminants, or rather of the kangaroo,