[17] Mantegazza, chap. vii., p. 119.
[18] Darwin believed that animals show their teeth in order to let their weapons be seen, and in this way to be more feared. This explanation does not seem to me quite exact, as animals are obliged to raise the lips when they bite, so that the soft parts of the mouth covering the jaws may not be injured. It suffices to watch a dog in order to convince oneself that the showing of the teeth must be an act preparatory to that of biting.
[19] Principles of Psychology, vol. ii., pp. 542-43.
[20] J. Müller: Handbuch der Physiologie des Menschen, 1840, ii. 92.
[21] Ch. Darwin: The Expression of the Emotions. London, 1872, p. 10.
[22] A. Mosso: Sui movimenti idraulici dell’ iride. R. Accademia di Torino, 1875.
[23] Ch. Darwin: The Expression of the Emotions, p. 225.
[24] G. B. Duchenne de Boulogne: Mécanisme de la Physionomie Humaine (Paris, 1862), p. 32.
[25] Edward C. Spitzka: Journal of Nervous and Mental Disease, 1879, s. 69.
[26] Mosso e Pellicani: Sulle funzioni della vescica. R. Accademia dei Lincei, vol. xii. 1881.