Oropharyngeal membrane, cloacal membrane
The embryo is trilaminar apart from the oropharyngeal membrane and the cloacal membrane. Ectoderm and endoderm border directly on each other with no mesoblast in between them. At S10, the oropharyngeal membrane (membrana oropharyngea) is observed. It marks off the foregut from the oral depression, and ruptures at S11. The cloacal membrane (membrana cloacalis) separates the hindgut from the anal depression. At S19, it begins to breaks down.

Primordial germ cells

Primordial germ cells arise from epiblast cells, which migrate out through the caudal region of the primitive streak. During the caudal flexion of the embryo, they migrate along the endoderm of the allantois and hindgut up to the genital ridges.