The human cranium has a browridge or supraorbital which it lies immediately above the orbits and inferior to the frontal squama. It begins in the region of glabella and arches smoothly over the orbit terminating at the frontozygomatic suture. Strong development of browridge will form a true supraorbital torus (SOT) that is a continuous bar of bone across both orbits and the nasal bridge. In addition, the morphology of the supraorbital region is greatly influenced by the masticatory system.
The great apes such as chimpanzee, gorilla and orang-utan have a browridge as well. Taxonomically, they are in the same group (superfamily) with humans, that is, hominoid. So, the human cranium possesses a browridge or supraorbital and so do the great apes. However, the supraorbital region of hominoids is variable and complicated. In African apes (chimpanzee and gorilla) the morphology of this region differs from that of the orang-utan. The former has stronger development of supraorbital region than the latter.
The supraorbital torus (SOT) in African apes and Homo can be divided into 3 regions: a central glabellar swelling that protrudes anteriorly; a medial portion of the arch between glabella and the superior orbital notch, known as the superciliary arch; and a more lateral portion between the supraorbital notch and the zygomaticofrontal suture, known as the supraorbital trigone.
In modern humans, browridge development is primarily limited to the medial segment, known as the superciliary arch. It is usually not developed in many modern children, adolescents and adult females. The lateral segment is also variable among living humans, ranging from no development to full development that combines with the medial segment to form a true supraorbital torus. The supraorbital torus can be existed among a small portion of modern humans. About 6.1% of Australian Aborigines exhibit such a condition. Tierra del Fueguians and Melanesians also often exhibit true supraorbital tori. Fossils of early anatomically modern humans tend to lack true supraorbital tori (SOT) and possess browridges that are divided into medial and lateral segments as do in the modern human crania.
Adult Neanderthal, Early and Middle Pleistocene hominid fossils generally exhibit supraorbital tori (SOT). Specimens of H.erectus from the Far East have a pronounced supraorbital torus that is straight, unarched and thickened towards the lateral aspect of the supraorbital trigone. The supraorbital torus of Neanderthal is different from that of H.erectus. Their supraorbital torus (SOT) usually forms a smooth convexity over each orbit and also there is tendency for torus to become thin laterally, rather than to thicken as it does in H.erectus crania. Neanderthal supraorbital torus are also extensively pneumatized by the frontal air sinuses, whereas those of H.erectus are less.
The characteristic of the morphology of browridge or supraorbital region is usually applied by scientists when they distinguished European Neanderthals from the modern human cranium because the anatomy of the supraorbital region differs dramatically between most modern humans and archaic humans such as Neanderthals.
References:
Aherna, J.C.M., and F.H. Smith. 2004. Adolescent archaics or adult moderns? Le Moustier 1 as a model for estimating the age at death of fragmentary supraorbital fossils in the modern human origins debate. HOMO—Journal of Comparative Human Biology 55: 1–19.
Aiello, L., and C. Dean. 1990. An introduction to human evolutionary anatomy. New York: Academic Press.
Relethford, J.H. 2005. The human species: an introduction to biological anthropology. New York: McGraw-Hill.
Stanford, C., J.S.Allen and S.C.Antón. 2006. Biological anthropology. New Jersey: Pearson Prentice Hall.
