Ectoplacental cone appears. Rapid increase in the number of inner cell mass cells leading to the formation of the epiblast with subsequent growth to form the egg cylinder. The proximal or visceral cells (opposite side from the trophoblastic cap) are cuboidal in shape. Primary endoderm lines the mural trophectoderm.  

5 dpc (range 4.5-6)  
Witschi Stage 10 (rat) 
Carnegie Stage 5 (human)

Scale bar in microns.