develops_from develops from surrounded by surrounded_by anatomical entity anatomical entity inner cell mass Blastocyst:English.svg This structure forms in the earliest steps of development, before implantation into the endometrium of the uterus has occurred.The ICM lies within the blastocyst cavity and is entirely surrounded by the single layer of cells called trophoblast. [Wikipedia:Inner_cell_mass] A mass of cells that develop into the body of the embryo and some extraembryonic tissues. EMAPA:16041 EFO:0000547 EHDAA2:0000830 EHDAA:40 A group of cells found in the mammalian blastocyst that give rise to the embryo. [Biology_Online][VHOG] Wikipedia:Inner_cell_mass A small sphere of cells known as the inner cell mass lies within the trophoblast (of all eutherian mammals).[well established][VHOG] VHOG:0000742 embryoblastus; massa cellularis interna; pluriblastus senior ICM uberon embryoblast early embryoblast UBERON:0000087 pluriblast NCIT:C13740 SCTID:361456007 FMA:86557 UMLS:C1283994 trophoblast blastocyst embryonic structure