wall

An inclosing or limiting structure. germinal w. That portion of the formative substance of the yolk that forms a ringlike thickening around the germinal disk, parietal w. The outer or upper composite sheet of the blastoderm, made up of the epiblast and the outer layer of the mesoblast. periotic w. The w. of the otic vesicle, splanchnic w. The inner layer of the blastoderm, made up of the hypoblast and the inner layer of the mesoblast. [Ang.-Sax., weal, a rampart.]