CHAP. V. MONKEYS. 133 we sometimes call silent laughter. Two of the keepers affirmed that this slight sound was the animal's laughter., and when I expressed some doubt on this head (being at the time quite inexperienced), they made it attack or rather threaten a hated Entcllns monkey, living in the same compartment. Instantly the whole expression of the face of the Inuus changed; the mouth was opened much more widely, the canine teeth were more fully exposed, and a hoarse harking noise was uttered. The Anubis baboon (Gynocepludus a nulls) was first insulted and put into a furious rage, as was easily done, by his keeper, who then made friends with him and shook hands. As the reconciliation was effected the ba- boon rapidly moved up and down his jaws and lips, and looked pleased. When we laugh heartily, a similar move- ment, or quiver, may be observed more or less distinctly in our jaws; but with man the muscles of the chest are more particularly acted on, whilst with this baboon, and with some other monkeys, it is the muscles of the jaws and lips which are spasmodical!)' affected. I have already had occasion to remark on the curious manner in which two or three species of Macacus and the Cynopitkeous niycr draw back their ears and utter a slight jabbering noise, when they are pleased by being caressed. With the Cynopithecus (fig. 17), the corners of the mouth are at the same time drawn backwards and upwards, so that the teeth are exposed. Hence this expression would never be recognized by a stranger as one of pleasure. The crest of long hairs on the forehead is depressed, and apparently the whole skin of the head drawn backwards. The eyebrows are thus raised a little, and the eyes assume a staring appearance. The lower eyelids also become slightly wrinkled; but this wrin- kling is not conspicuous, owing to the permanent trans- verse furrows on the face.