Former and present aspects in upper level of viscero-skull architecture.

The classical reference material describes two resistance arcs, the maxillary arc and the mandibulary arc, from which the masticatory forces direct themselves towards the functional resistance structures of the viscero-skull. From the maxillary arc, three pairs of vertical pillars ascend (that is fronto-nasal, zygomatic and pterygoid). Certain authors add to these a median arc--the bony part of the nasal septum. From the mandibulary arc, the lines of force make for the cordyle and the coronoid process of the mandible. In terms of the new outlook, at the upper level of the viscero-skull, there are five vertical blades described: one median, two medial and two lateral, those last including the pillars from the classical descriptions. These vertical blades are joined by three horizontal laminae: the upper one, the middle one--interrupted by the median line and the lower one--included in the concavity of the maxillary arc. These structures of laminae induce the formation of some resistance cylinders and cones. Within the lower level of the viscero-skull there are three mandibulary arcs described: the upper one (the classic mandibulary arc), the middle one (with an oblique direction) and the lower one.