The process in which a mesodermal, bone marrow or neural crest cell acquires specialized features of an endothelial cell, a thin flattened cell. A layer of such cells lines the inside surfaces of body cavities, blood vessels, and lymph vessels, making up the endothelium. [ http://purl.obolibrary.org/obo/CL_0000115 GOC:go_curators ]
This is just here as a test because I lose it