Dr. Steinmann Henrik szerk.: Folia Entomologica Hungarica 23/1-12. (Budapest, 1970)

tion the mandible of the insects (defined only erroneously as the upper jaw) executes a horizontal movement during its milling action. In insects with a non-gnawing type of oral organs the role of the mandible diminished and the structure had extensively modified and degenerated. The muscles of the mandibular region are shown in Fig.l. The strongest and greatest mass of muscles are represented by those of the mandible in the insect head. Four kinds of mandibular groups of muscles can be distinguished, of which the musculus abductor and the musculus adductor comprise the greatest volume. Corresponging to the variously developed and robust mandibles of diverse roles, the muscles cited above will also differ. It can be seen in Fig. 3. that the muscles moving the mandibles do not act, similarly to the alar muscles, directly on the mandible but on the chitinous structures supporting the mandible proper. The contraction and relaxation of the muscles, filling the major part of the cephalic case, bend the mandibles inwards and outwards,respectively (m - 12 and m - 14). In the act of gnawing, the solidifying chitinous bundles of the head, the tentorium, also have a decisive role. The placing and holding of the food between the mandibles as well as its introduction to the oral opening are primarily done by the maxilla and its palps. The muscles of the mandible are: m - 11: musculus hypopharyngeo-mandibularis m - 12: musculus adductor mandibularis m - 13: musculus tentorio-mandibularis m - 14: musculus abductor mandibularis The first main nerve trunk of the ganglion infraoesophageum (Fig. 2), the nervus mandibularis, emits, soon after its origin from the nerve centre, the so-called adductorial nerve trunk containing a number of motoric (n - 12) and one or more sensory nerves (nervus mandibularis adductor). Decurrent towards the mouth or the mandible, the main nerve trunk emits the nerve of the musculus hypopharyngeo-mandibularis (n - 11), then it may