Probabilistic finite element analysis was used to determine whether there is a statistically significant relationship between maximum principal strain orientations and orthotropic material stiffness orientations in a primate cranium during mastication. We first sought to validate our cranium finite element model by sampling in-vivo strain and in-vivo muscle activation data during specimen mastication. A comparison of in vivo and finite element predicted (i.e. in silico) strains was performed to establish the realism of the FEM model. To the best of our knowledge, this thesis presents the world’s only complete in-vivo coupled with in-vitro validation data set of a primate cranium FEM. Our results indicate that a validated FEM of a Cebus apella cranium was achieved. Giving collaborating anthropologists, biologists, and engineers the confidence that these models have sufficient accuracy to address the research questions pertaining to cranial structure morphology. Probabilistic finite element analysis design was then utilized to determine the dependence of maximum principal strain orientations on material stiffness orientations in particular craniofacial regions during mastication. It was discovered that the maximum principal strain orientations are more dependent on loading conditions and/or the shape of and location in the cranium rather than the material stiffness orientation of a particular region. It was also uncovered that the material stiffness orientations are not developed in a way that is optimal for feeding biomechanics from the perspective of minimization of total elastic strain energy. Results from this research will provide insights into the co-evolution of bone morphology and material properties in the facial skeleton.