A new functional classification of muscles, determining movements of the mandible is presented. This classification reflects anatomo-topographic and histogenetic peculiarities of the muscles in question. Their functional differentiation in phylogenesis is motivated, coming from specific tasks they perform. Two groups of muscles of direct and mediated action on the mandible are distinguished. The groups are divided into functional subgroups. Mathematical correlations between various subgroups of the muscles at normal functioning of the mandible are presented. This makes possible to perform calculations of the acting muscle forces at planning reconstructive operative interventions in the maxillofacial area.