bone may retain its
normal position in line with the alveolar processes of the maxilla
(Fig. 234), or it may be tilted forward so that the incisor teeth,
when present, project beyond the level of the prolabium (Fig. 235). In
aggravated cases, the os incisivum and prolabium are adherent to the
end of the nose. In these cases there is a Y-shaped cleft in the
palate.

[Illustration: FIG. 234.--Double Hare-lip in a girl aet. 17.]

[Illustration: FIG. 235.--Double Hare-lip with Projection of Os
Incisivum, in an infant before first dentition.]

#Cleft Palate.#--It has already been mentioned that the palate is
formed by the blending of the two palatal plates of the maxillary
processes with the four segments of the os incisivum, derived from the
nasal processes. The foramen incisivum (anterior palatine foramen)
marks the point at which these elements of the palate unite. The
process of fusion begins in front and spreads backwards, the two
halves of the uvula being the last part to unite.

As development may be arrested at any point, several varieties of
cleft palate are met with. The uvula, for example, may be bifid, or
the cleft may extend throughout the soft palate. In more severe cases,
it extends into the hard palate as far forward as the foramen
incisivum. In these varieties the whole cleft is mesial. In still more
aggravated cases, the cleft passes farther forward, deviating to one
or to both sides in the fissures between the mesial and lateral
segments of the os incisivum or between the lateral segments and the
maxillae. These cases are combined with double hare-lip.

The cleft varies considerably in width. It may be so wide that the
imperfectly developed nasal septum is seen between its edges, and
gives to the cleft the appearance of being double, or the septum is
adherent to one edge of the palate--usually the right--and the cleft
appears to be to the left of the middle line. In most cases the roof
of the mouth is unduly arched, and is narrower than normal (Fig. 236).

[Illustration: FIG. 236.--Asymmetrical Cleft Palate extending through
alveolar process on left side.]

_Clinical Features._--_Single hare-lip_ is about twice as common on
the left as on the right side, and it occurs more frequently in boys
than in girls. In a considerable proportion of cases there is a
well-marked hereditary tendency to these deformities, and they
frequently occur in several members of a family.

The nose is characteristically