THE DIGESTIVE APPARATUS. The Mouth is a cavity formed by the
lips in front, cheeks at the side, tongue below, and palate
above. The roof of the mouth derives its bony part from the
upper jaw-bone on each side and the palate bones behind (see p.
60); the bone is covered by the mucous membrane (c, Fig. 101) of
the mouth. Reference to Fig. 101 will show that the bone (a)
forms only the front por tion of the palate—the hard palate, as
it is called, —for the bone stops short at b, and the con
tinuation is effected by mucous membrane and muscular substance
as the soft palate, of which the uvula (u) is a part. The hard
and soft palates form not only the roof of the mouth but also
the floor of the cavity of the nose (a, Fig. 101), so that they
partition off the nose from the mouth. Now sometimes this
partition is not properly developed, and a cleft exists in the
soft palate. The cleft may extend forwards some distance and may
involve the hard palate, so that the partition is incomplete and
an opening more or less wid