Oral development in the embryo is demarcated
very early with the appearance of the prochordal
plate in the bilaminar germ disc on the
14th day of development. This structure later contributes to the temporary
buccopharyngeal membrane. This membrane is the junction between the ectoderm
which will form the mucosa of the mouth and the endoderm
which will form the mucosa of the pharynx - the most anterior part of the
foregut. Mesoderm never penetrates between
these germ layers here. The buccopharyngeal membrane is in a shallow depression
- the stomodeum, or primitive mouth which is
an important landmark in the developing face. Until the end of the 4th
week of development, the head is a relatively featureless structure. The
face forms in weeks 5-9. The deeper oral cavity is formed by the forward
growth of the facial processes (see on) around the stomodeum and the buccopharygeal
membrane disintegrates around the end of the 4th week permitting continuity
between the mouth and pharynx.
The early embryo has a common oronasal
cavity but the palate forms to separate it into oral and nasal components.
A primary and a secondary palate form and the definitive palate is completed
by about week 11. It is useful to know the normal embryology of palatal
development in order to understand how it can go wrong. |
