Early embryology of the prechordal region

الملخص EN

Background: Prechordal plate is important midline structure in the head region.

It has been shown that it plays a bivotal role in the development of the brain and the eyes.

Aim of study: There is confunsion, in the literatures and textbooks concerning of terms: prechordal plate, prechordal mesoderm and the Buccopharyngeal membrane.

The aim of this work is to study is based on histological changes of the early stages of the chick embryo hoping to illuminate these aspects especially after the recent revival of attention to the importance of this region in the process of induction of the brain region of the newral tub & the development of the prosencephalon & the eyes as shown by genes activities & expression in the prechordal plate ..

Materials & Methods :this study is based on histological description of the early stages (4- 7H.&H.) of the chick embryo to illuminate the nature of these structures .

It appeared that the cephalic foregut in the early stages is lined by tall endodermal cells that form three regions: Dorsal wall (PI) where it forms the prechordal plate and contributes to the formation of the prechordal mesodermal mass (mesoendoderm); the rostral end (P2), and the ventral wall (P3) where it fuses with the surface ectoderm forming the oral plate (or the Buccopharyngeal membrane).

The contribution of endoderm to the head mesenchyme is emphasized in this study.

Conclution: this study indicated that the prechordal plate is not simply the Buccopharyngeal membrare it forms an early proliferating zone , rostal to the notochord , that contribute to the mass of prechordal mesoderm & another zone , which is extending later as a Sessels pouch , which also proliferate for some time .

also the ventral extension is a part of Buccopharyngeal membrane.