<P> Oyen et al. conducted a cross-section study of Papio anubis in order to ascertain the relationship between palate length, incisor load and Masseter lever efficiency, relative to torus enlargement . Indications found of osteoblastic deposition in the glabella were used as evidence for supraorbital enlargement . Oyen et al.'s data suggested that more prognathic individuals experienced a decrease in load / lever efficiency . This transmits tension via the frontal process of the maxilla to the supraorbital region, resulting in a contemporary reinforcement of this structure . This was also correlated to periods of tooth eruption . </P> <P> In a later series of papers, Russell developed aspects of this mode further . Employing an adult Australian sample, she tested the association between brow ridge formation and anterior dental loading, via the craniofacial angle (prosthion - nasion - metopion), maxilla breadth, and discontinuities in food preparation such as those observed between different age groups . Finding strong support for the first two criteria, she concluded that the supraorbital complex is formed as a result of increased tension due to the widening of the maxilla, thought to be positively correlated with the size of the masseter muscle, as well as with the improper orientation of bone in the superior orbital region . </P> <P> The brow ridge functions to reinforce the weaker bones of the face in much the same way that the chin of modern humans reinforces their comparatively thin mandibles . This was necessary in pongids and early hominids because of the tremendous strain put on the cranium by their powerful chewing apparatuses, which is best demonstrated by any of the members of the genus Paranthropus . The brow ridge was one of the last traits to be lost in the path to anatomically modern humans, and only disappeared in a majority of modern humans with the development of the modern pronounced frontal lobe . This is one of the most salient differences between Homo sapiens and other species like the Homo neanderthalensis . </P> <P> The size of these ridges varies also between different species of primates, either living or fossil . The closest living relatives of humans, the great apes, have a relatively pronounced supraorbital ridge, which has also been called a frontal torus while in modern humans it is relatively reduced . The fossil record indicates that the supraorbital ridge in early hominins was reduced as the cranial vault grew; the frontal portion of the brain became positioned above rather than behind the eyes, giving a more vertical forehead . </P>

What is the purpose of the brow ridge