Cleft palates are comparatively rare in proportion to other forms of nutritive degeneracy. Palatal embryology casts light on the causation. At a very early period of foetal life a series of clefts appear on each side of the cephalic extremity, separated by rods of tissue called branchial arches. The clefts communicate with the alimentary canal. These various clefts have usually coalesced about the ninth and tenth week of foetal life, but occasionally this coalescence fails or is incomplete. This leads to various deformities, the chief of which are cleft palate and hare-lip. Cleft palate has been known to affect several members of the same family, and to occur in the offspring of the affected members. There are instances of the transmission of this deformity from an affected pug-bitch to her offspring. If it were possible to practise selective breeding in man as in dogs a race of men with hare-lips and cleft palates could probably be produced.[201] [Illustration: FIG. 31.] Cleft palate may be divided into two classes, congenital and acquired, acquired cleft palate being the result of disease either inherited or acquired, but only affecting the part after birth. Congenital cleft palate is divisible into two kinds, complete and partial; complete when the fissure extends the entire length, from the uvula to and including the anterior alveolar process and even the lips (Fig. 31), partial when only a small part of the structure is involved. Thus the cleft may extend through the anterior alveolar process, involving the incisive bone only, which is very rare; when present single or double hare-lip almost invariably coexists. I have observed in practice six cases where a small portion of the interior alveolar process was involved, with the jaw and one or two teeth. The hard palate only may be involved to the extent of a small fissure, or the whole palate may be wanting. The soft palate only may contain the cleft, or simply the uvula. Cases are on record in which the non-development of the intermaxillary bones produces fissures in the lip. _A priori_, cleft palate is an evident expression of hereditary defect. Langdon Down found a constant relation between brain deformity, cleft palate, and deformed vaults. In a case cited elsewhere,[202] three members of one family had cleft palate; one 17 years old, the other 30, and the third 35. The first and last are women, the other a married man with a family, who have no trace of the father's deformity. In these cases no instance of cleft palate could be found either among the ancestors or the collateral branches of the family. Another family has a remarkable history. G. H. C., born 1853, perfect; L. C., born 1855, single hare-lip and cleft palate; J. F. C., born 1856, perfect; F. W. C., born 1860, double hare-lip and cleft palate; H. E. C., born 1868, perfect. The paternal grandmother also had cleft palate.