ANATOMY

Detailed explanation-1: -The ultrastructure of the oral (buccopharyngeal) membrane in the embryo of the urodelan, Hynobius tokyoensis, was examined by transmission (TEM) and scanning electron microscopy (SEM). The oral membrane consists of the stomodeal ectoderm and foregut endoderm, and is three to five cell layers thick at stage 24.

Detailed explanation-2: -It is created from the cranio-caudal and lateral folding of the embryo, resulting in the incorporation of one portion of the endoderm-lined yolk sac into the embryo to form the primitive gut. The other two portions of the endoderm-lined cavity, the yolk sac and the allantois, remain outside of the embryo.

Detailed explanation-3: -2 The ectoderm and endoderm that form the middle of the stomodeum thin-each becoming a single layer2, 5 (Figure 6(b)). These layers intercalate to form a one or two cell thick ‘buccopharyngeal membrane, ’ which perforates to open the mouth (Figure 6(b), st. 40).

Detailed explanation-4: -The notochordal process grows cranially until it reaches the prechordal plate, the future site of the mouth. In this area the ectoderm is attached directly to the endoderm without intervening mesoderm. This area is known as the oropharyngeal membrane, and it will break down to become the mouth.

Detailed explanation-5: -The oropharyngeal membrane is composed of cells from both the ectoderm and endoderm, but not from the mesoderm. Thus, cells from the germ layer mesoderm are not present in the oropharyngeal membrane.