Non-material anatomical entity
of two dimensions, that is demarcated by anatomical lines or points on the external or internal surfaces of anatomical structures.
written by: Haendel, M. A., F. Neuhaus, D. Osumi-Sutherland, P. M. Mabee, J. L. V. Mejino, C. J. Mungall, and B. Smith. 2008. CARO - The Common Anatomy Reference Ontology. Pp. 311-333 in: Anatomy Ontologies for Bioinformatics: Principles and Practice; Burger, A, Davidson, D, Baldock, R (Eds.). Springer. 356 pp.