The cephalic index or cranial index, the ratio of the maximum width (biparietal diameter or BPD, side to side) of the head of an organism multiplied by 100 and then divided by their maximum length (occipitofrontal diameter or OFD, front to back). The index was once used to categorize human beings in the first half of the 20th century, but today it is used to categorize dogs and cats. Historic use in anthropology Early anthropology The cephalic index was used by anthropologists in the early 20th century as a tool categorize human populations. It was used to describe an individual's appearance and for estimating the age of fetuses for legal and obstetrical reasons. The cephalic index was defined by Swedish professor of anatomy Anders Retzius (1796–1860) and first used in physical anthropology to classify ancient human remains found in Europe. The theory became closely associated with the development of racial anthropology in the 19th and early 20th centuries, when historians attempted to use ancient remains to model population movements in terms of racial categories. American anthropologist Carleton S. Coon also used the index in the 1960s, by which time it had been largely discredited. In the cephalic index model, humans beings were characterized by having either a dolichocephalic (long-headed), mesaticephalic (moderate-headed), or brachycephalic (short-headed) cephalic index or cranial index. Indices Cephalic indices are grouped as in the following table: Technically, the measured factors are defined as the maximum width of the bones that surround the head above the supramastoid crest (behind the cheekbones), and the maximum length from the most easily noticed part of the glabella (between the eyebrows) to the most easily noticed point on the back part of the head. Controversy The usefulness of the cephalic index was questioned by Giuseppe Sergi, who argued that cranial morphology provided a better means to model racial ancestry. Also, Franz Boas studied the children of immigrants to the United States in 1910 to 1912, noting that the children's cephalic index differed significantly from their parents', implying that local environmental conditions had a significant effect on the development of head shape. Boas argued that if craniofacial features were so malleable in a single generation, then the cephalic index was of little use for defining race and mapping ancestral populations. Scholars such as Earnest A. Hooton continued to argue that both environment and heredity were involved. Boas did not himself claim it was