The region where the crescentic masses of the ectoderm and endoderm come into direct contact with each other constitutes a thin membrane, the buccopharyngeal membrane (or oropharyngeal membrane), which forms a septum between the primitive mouth and pharynx.
A thin membrane, referred to as the buccopharyngeal membrane (or oropharyngeal membrane), forms at the junction of crescentic masses in ectoderm and endoderm. This membrane serves as a partition between the primitive mouth and pharynx.