Retzius, Anders Adolf (1796–1860), Swedish anatomist and anthropologist. A professor of anatomy and physiology in Stockholm, Retzius conducted his early research in comparative anatomy, of which he was a pioneer in Sweden. An early discovery was an organ of elasmobranch fishes homologous with the adrenal cortex of higher animals. His investigations of the chordate amphioxus were very important in the development of comparative anatomy and embryology. Retzius is best known for his pioneering studies in craniometry, however. In 1842 he devised the cranial index, which is based upon the ratio of the skull's width to its height and serves as a preliminary indicator of racial identity for human fossils.