immaterial anatomical entity anatomical surface A two dimensional anatomical structure that is the boundary between an anatomical structure and an anatomical substance, an anatomical space or the organism's environment. Examples include the surface of your skin, the surface of the lining of your gut; the surface of the endothelium of you aorta that is in contact with blood.n AAO:0010270 BILA:0000010 CARO:0001002 EHDAA2:0003192 FMA:24137 ID:0000000 Old definition: 'Non-material anatomical entity of two dimensions, that is demarcated by anatomical lines or points on the external or internal surfaces of anatomical structures.' Note, in the new definition, the space referred to is not necessarily an anatomical space. It may be the outside of an organism. UBERON:0006984 UMLS:C1515977 ZFA:0005594 uberon