M any of the present-day views on tongue-thrusting are reflected in the early writings of very able clinicians, and their work has to some extent been ignored. Like many other present-day views on orthodontics, they have gone through a full cycle, and in the conclusion to this article it will be sepn t,hat there has been an overconcentration on the effect of the soft tissues on malocclusion. One of the earliest writings is that of Lcf~ulon,~ published in 1839, in which it is obvious that he appreciated t,hat among the causes of irregularities of teeth wcrc “sounds of speech in which the tongue strikes against the upper anterior teeth, pushing them forward.” An article by Desirabode,” published in 1843, is the first traceable refercncc to the fact that the lips on the outside and the tongue on the inside of the mouth constitute a balance of forces that may retain the teeth in their position. In 1859, Bridgeman” introduced the “lateral pressure theory” and described irregularities of the teeth due to visincreme~ati (external muscle forces, as that of the lips and cheeks), visestensionis (internal muscle forces, as that of the tongue), and wisoccZusioS (occlusal forces). Kingsley,4 in 1879, made a considerable study of speech sounds but did not relate movements of the soft tissues to dental arch form. At the turn of the century, Angle5 recognized the problems of the muscular environment of the dental arches but would not accept the fact that in certain cases t,hey might form an insurmountable difficulty in treatment. In the appendix to the seventh edition of Malocclusion of the Teeth, Angle states : “We are just beginning to realize how common and varied are the vicious habits of the lips and tongue, how powerful and persistent they are to overcome.” Norman Bennett6 showed a clear understanding of the problem when, in 1914, he wrote: “The muscles of mastication produce conditions of vertical and lateral stress, the USC of the tongue in mastication and speech reacts upon the teeth internally, and the lips and cheeks in their every movement, even of