part of part of develops_from surrounded_by morula inner cell mass 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] 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] 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 FMA:86557 UMLS:C1283994 A mass of cells that develop into the body of the embryo and some extraembryonic tissues trophoblast blastocyst embryo embryonic structure