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THE DENTAL RIDGE AND DENTAL GROOVE. 55

Fig. 32.

Section of jaw, embryo of pig, showing the epithelium highly magnified: 1, oldest epithelial
cells ; 2, the younger cells ; 3, the infant layer, the stratum Malpighii ; 4, the embryonic connec-
tive tissue.
The epithelium, as has been stated, is derived from tlie epiblast, and
is developed considerably earlier than is the embryonic connective tis-
sue beneath.

The Dental Ridge and Dental Groove.
On that portion of the jaw which is to become the alveolar border,
between the fortieth and forty-fifth days,
Fig. 33.
there is seen a growth of cells, which looks
as though it had been pushed up in the
form of a smooth ridge. If a section is
cut across the jaw at this time, and exam-
ined, it will be found that this ridge con-
sists of a mound of epithelial cells which
some writers have called the maxillary
rampart. This growth of cells is seen to
have had a more energetic growth inward
into the substance of the embryonic tissue
tlian it has had outward, so that a groove
containing epithelium is formed around the Section thr<.ui,'h ilic jaws of human
entire upper border of the jaw, and in this embryo, showing developing en-
amel organs. (Section by Dr.
condition has been called the tooth band. Sudduth.)