Carnegie Stage 5a-2

Introduction

The older stage 5a specimen is Carnegie embryo #8155 that has an estimated postfertilization age of 8 days. The conceptus shows later superficial implantation being almost imbedded within the endometrium and nearly flush with the endometrial epithelium. The amniotic cavity is prominent and amnioblast are present. The embryonic disc is dorsally concave. The epiblast is composed of pseudostratified columnar eipithelium with only one mitotic figure evident. The hypoblast is composed of a cap like mass of smaller polyhedral cells with large nuclei that nearly fill each cell.