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Show 202 EXPRESSION OF JOY: CrrAP. VIII. a much less degree than when tickled by another person, it seen1s that the precise point to be touched must not be known ; so with the mind, something unexpected-a novel or incongruous idea which breaks through an habitual train of thought-appears to be a strong element in the ludicrous. The sound of laughter is produced by a deep inspiration followed by short, interrupted, spasmodic contractions of the chest, and especially of the diaphragm.8 Hence we hear of "laughter holding both his sides." From the shaking of the body, the bead nods to and fro. The lower jaw often quivers up and down, as is likewise the case with some species of baboons, when they are much pleased. During laughter the mouth is opened more or less widely, with the corners drawn much backwards, as well as a little upwards; and the upper lip is somewhat raised. The drawing back of the corners is best seen in moderate laughter, and especially in a broad smilethe latter epithet showing how the mouth is widened. In the accompanying figs. 1-3, Plate III., different degrees of moderate laughter and smiling have been photographed. The figure of the little girl, with the hat, is by Dr. Wallich, and the expression was a genuine one ; the other two are by Mr. Rejlander. Dr. Duchenne repeatedly insists 9 that, under the ernotion of joy, the mouth is acted on exclusively by the great zygoInatic muscles, which serve to draw the corners backwards and upwards ; but judging from the manner in which the upper teeth are always exposed during laughter and broad smiling, as well as from my own ~ensations, I · cannot doubt that some of the muscleR 8 Sir C. Bell (Anat. of Expression, p. 147) makes some 1·emarks on the movement of the diaphragm during laughter. 9 ' ~1ecani~me qe l~ Physionomie l:lumaine,' Albun~, Legoncle vi, I J 6 |