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. In front of the buccopharyngeal area, where the lateral crescents of mesoderm fuse in the middle line, the
pericardium is afterward developed, and this region is therefore designated the
pericardial area.