[Problems posed by the orientation of the head]

After a brief history of the origin of the planes of section of the head, the authors state that there are two kinds of planes: "convenient" planes and those with a scientific basis. Among the latter, they study those which are based on the sensory organs and in particular, on sight (Broca's alveolocondylian plane) and balance (plane of the lateral semi-circular canal or its branches). The positioning of the head cannot be the result of a single sensory organ and even less of one part of a sensory organ. This positioning results from informations given by nearly all sensory organs.