The muscles of the chin collaborate with other facial muscles in expressional movement, and are similarly liable to be the seat of tics. Massaro[73] has observed an interesting series of isolated "geniospasm" occurring in twenty-six individuals of the same family during five generations. The characteristic feature of these spasms was an involuntary intermittent clonic contraction of the transverse muscles of the chin, suggesting the look of one seized with fear or with cold. The will did not always effect their inhibition, while emotion appeared to aggravate and distraction to abate their intensity. With sleep they vanished entirely. TICS OF THE TONGUE--LICKING TICS Tics confined exclusively to the tongue are of rare occurrence. Moreover, they must be strictly differentiated from the tonic or clonic contractions of the tongue muscles met with in hysteria, epilepsy, and Sydenham's chorea, from the varying tremors that accompany organic disease of cerebral or bulbo-pontine origin, as well as from those "glosso-spasms" that may or may not be associated with twitches of the facial musculature. Functional polymorphism is no less marked in the case of the tongue than in that of the lips; it participates in suction, mastication, deglutition, as well as in respiration, phonation, and articulation, while to "put out the tongue" at any one is equivalent to an expression of contempt. It is, accordingly, no surprise to find the number of tongue tics very considerable. Such, for instance, is the licking tic, where the tongue is constantly being passed over the free border of the lips, moistening them to excess; or the chewing tic, in which its perpetual motion inside the mouth in every direction conveys the impression that the subject is chewing something. Further, its contact with the palate or the upper lip may yield different clucking, whistling, or crowing sounds. Letulle remarks that the trick of producing a little inspiratory whistle by the passage of a column of air through an incompletely closed labial commissure--a common habit among people suffering from dental caries--is not slow in developing into an actual tic.