Plates 30, 31, 32, 33, 34, 35, 36

(Compare alternately the two sides of Plates 30, 35 and 36, by masking the opposite side.)

Plate 30: To study the fundamental and secondary expressive lines produced by the contraction of m. zygomaticus major in an old man (shown also in Plates 3, 6, 7, 8, 9, 12, 13, 14, 17, 18, 19, 20, 21, and 22). On the right, electrical excitation, which is strong but quite limited to m. zygomaticus major, showing development of the fundamental and secondary lines of this muscle: false joy or laughter. On the left, a relaxed face.

Plate 31: Slightly stronger electrical excitation of both mm. zygomaticus major: development of the same fundamental and secondary expressive lines of joy, with mild contraction of some fibers of the muscle called the sphincter of the eyelids: false laughter.

Plate 32: The same subject as in Plates 30 and 31, showing that natural laughter really is constituted by the association of m. zygomaticus major and the inferior part of m. orbicularis oculi. Natural laughter, by the voluntary contraction of the two mm. zygomaticus major and of the inferior part of mm. orbicularis oculi.

Plate 33: The same subject, showing that the wrinkles radiating from the lateral canthus of the eyelids, due to the action of mm. zygomaticus major, disappear when mm. frontalis is stimulated at the same time. Maximal stimulation of mm. zygomaticus major and of mm. frontalis: a false incomplete expression of agreeable surprise, or admiration. […]