Spatial model for brow ridge formation

Much of the groundwork for the Spatial model was laid down by Schultz (1940). He was the first to document that at later stages of development (after age 4) the growth of the orbit would outpace that of the eye. Consequently, he proposed that facial size is the most influential factor in orbital development, with orbital growth being only secondarily affected by size and ocular position.

Weindenreich (1941) and Biegert (1957, 1963) argued that the supraorbital region can best be understood as a product of the orientation of its two components, the face and the neurocranium.

The most composed articulation of the spatial model was presented by Moss and Young (1960), who stated that “the presence… of supraorbital ridges is only the reflection of the spatial relationship between two functionally unrelated cephalic components, the orbit and the brain” (Moss and Young, 1960, p282). They proposed (as first articulated by Biegert in1957) that during infancy the neurocranium extensively overlaps the orbit, a condition that prohibits brow ridge development. As the splanchocranium grows, however, the orbits begin to advance, thus causing the anterior displacement of the face relative to the brain. Brow ridges then form as a result of this separation.

To put it simply, the Spatial model proposes that supraorbital torus development can be best explained in terms of the disparity between the anterior position of the orbital component relative the neurocranium.

References

Schultz, AH (1940) The size of the orbit and eye in primates. American Journal of Physical Anthropology. 26:389-408.