Definition: "Blastomere which lies lateral to blastomere V1.1.1 and is in the first tier of blastomeres. It contributes to many ectodermal structures including the epidermis, lens, cranial ganglia, otic vesicle, neural crest, olfactory placode, cement gland, retina, brain, and spinal cord. It also contributes cells to the pharyngeal mesoderm, head mesenchyme, heart, somites, pronephric kidney, lateral plate mesoderm and tail fin mesenchyme, archenteron roof, with occasional cells in the foregut, liver, hindgut and proctodeum."