Supraorbital ridge

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Supraorbital ridges seen in Australopithecus africanus

The supraorbital ridge, supraorbital torus, superciliary ridge, arcus superciliaris, or brow ridge, refer to a bony ridge located above the eye sockets of all primates. In Homo sapiens sapiens (modern man) the eyebrows are located on their lower margin. Gray's Anatomy says:

"Below the frontal eminence" (forehead) "and separated from it by a slight groove, is the superciliary ridge .... Beneath the superciliary ridge is the supraorbital arch, a curved and prominent margin, which forms the upper boundary of the orbit ...." During puberty, male's supraorbital ridges grow to be more pronounced than the female's.

1 Anthropological concept
2 Theories and myths
3 In modern humans
4 Notes
5 See also
6 External links

[edit] Anthropological concept

The size of these ridges varies also between different species of Primate, either living or fossil. The closest living relatives of man, the Great Apes, have very pronounced supraorbital ridges. The evolution of man therefore is thought to have included a gradual reduction of the ridges. The size of the ridges is typically used as a rough indicator of date and therefore of stage of evolution.

Some palaeanthropologists distinguish between "torus" and "ridge." In anatomy a torus is a projecting shelf of bone.^[1] Fossil hominids, in this theory, have the torus, but modern humans only have the ridge.

Gorilla face.

Chimpanzee face.

[edit] Theories and myths

The purpose of the ridges is strictly conjectural. Their protective value is manifest, and they may help to keep sweat and sun out the eyes, but the factors bearing on the variation in their size between different species and within the human species remain unknown. The folk-myth that the size of the ridges is a mark of the degree of development of rationality has no basis in fact. There is no known link between the size of the ridges and any other anatomical trait, including intelligence.

[edit] In modern humans

Some varieties of modern man have more pronounced ridges than others; for example, indigenous Australians, conventionally termed "aborigines."

Some faces of non-European Australians ca. 1914. The slightly more pronounced ridges can best be seen in profile.

[edit] Notes

^ For some basic English definitions refer to the American Heritage Dictionary online under supraorbital and torus. Webster's Third New International Dictionary also does not make the distinction.