composed primarily of Homo sapiens connective tissue organ component layer adventitia http://upload.wikimedia.org/wikipedia/commons/e/e8/Illu_esophageal_layers.jpg tunica advetitia SCTID:30180000 tunica externa MESH:D063194 An outermost connective tissue covering of an organ, vessel, or other structure[WP]. Wikipedia:Adventitia BTO:0002010 UBERON:0005742 FMA:45635