Pneumatized spaces, sinuses and spongy bones in the skulls of primates.

The earliest attempts to understand the "pneumatized spaces" in the skulls of primates in general were focussed on the hollow spaces and the epithelium which covers their surfaces. More recent approaches consider the sinuses as a means to optimise skull architecture. Still, many attempts to get hold of the meaning of the intriguing pneumatized spaces circle around the air filled volumes they enclose. Here, we would like to reverse the approach and focus our biomechanic interpretation on the walls surrounding the big, empty, or at least not mechanically resistant spaces, and their mechanical properties. As a working hypothesis, we consider not only the walls of the more or less closed cavities, or sinuses, but also the braincase, the orbits, and the nasal channel as thin-walled shells of which we know that they can carry surprisingly large loads with a minimum of material. Details of the wall's profiles fit with this approach. From the same viewpoint, the bubble-like, air-filled cavernous systems in the ethmoid or temporal bones, and the marrow-filled spongy substance in the upper jaw are looked at as honeycomb-structures, which provide mechanical properties that are biologically advantageous and allow the saving of weight.