The diversity of movement of which the buccal orifice is capable warrants the statement that the tics of this class are almost too numerous for detailed description. At times only the orbicularis oris is involved, unilaterally or bilaterally; at others, concomitant implication of the elevators and depressors of the lips, or of the chin muscles and the platysma, furnishes the basis for all sorts of pouting, biting, and sucking movements, and for every variety of smile and grin. Here again the clonic form of contraction is the most habitual, although that rapidity and abruptness which we commonly identify with such contractions may not always be conspicuous. Guinon says of a young patient of his, at one time addicted to innumerable tics, that the relative sluggishness with which she opened and shut her mouth served to inspire belief in the reality of the tonic tic of certain authors. As a matter of fact, tonic tics do exist, and are sometimes associated with another variety known as mental trismus, to the discussion of which we shall revert ere long. The action of the muscles of the lips is manifold: whether in the expression of the emotions, or in the discharge of different functions, they come into play in miscellaneous modes that may be the forerunners of a multiplicity of tics. Of these, two types may be distinguished, according as expansion or occlusion of the labial orifice predominates. Under the one heading; come the caricatures of ordinary smiling or laughing, under the second those that exaggerate the pursing or pouting movements whereby we are wont to indicate chagrin, repugnance, disdain, etc. Labial tics of this nature may be styled tics of facial mimicry. In the infant that has long been weaned, and _a fortiori_ in the adult, the continuance of the act of sucking must of course be considered a functional anomaly; and while no doubt it is true we use our lips in imbibing a beverage through a straw, or in extracting the juice from a fruit, the action is different from that of the infant, and in any case not to be compared with incessant sucking of tongue or thumb, or of some object devoid of all nutritive value--merely a bad habit, perhaps, but frequently indistinguishable from tic. The most fruitful source of the tics under consideration is to be found in labial cracks and dental mischief. More especially in children, towards the end of the first dentition, the torment of loose teeth calls forth interminable devices for relief, in seeking which tongue and lips pleasurably co-operate. Once the tooth is out, the lacuna it leaves provides a new sensation and a new reason for muscular activity. Irregularity of the permanent teeth may also be referred to as a potent factor in the causation of tic. It is therefore not superfluous systematically to examine the teeth of all patients suffering from tics of the mouth, and to extract any offender. TICS OF THE CHIN