A morphogenetic model of cranial pneumatization based on the invasive tissue hypothesis.

The interpretation of patterns of cranial pneumatization in terms of evolution, development, and function is controversial, because these structures exhibit extreme diversity and variability among and within taxa. However, there is general consensus that air-filled spaces are formed by invasion of mucous epithelial tissue from the nasopharyngeal cavity into the surrounding cranial bones. This investigation presents a morphogenetic model of pneumatization, which combines empirical data about epithelial growth with physical concepts of surface growth. The study develops a model that defines growth equations with a minimum number of system parameters to simulate the invasion of mucous tissue and air-filled spaces into the cancellous compartment of cranial bones. Computer simulations show that tuning a small set of model parameters permits generation of a wide diversity of morphologies mimicking natural air-filled spaces. Comparison of virtual with actual morphologies yields new insights into possible factors controlling the process of cranial pneumatization.