Fig. 3. Morphology of normal HMEC grown in MM. A, confluent 2^nd passage cells with typical epithelial cobblestone morphology continuing in the confluent populations. (Magnification X 180.) B, confluent 4^th passage cells. Note the heterogeneity in cell morphology, with areas of small refractile growing cells, tightly packed areas of small nongrowing cells, and large squamous vacuolated cells. (magnification X 45).