[Tomographic incidence of the petrous bone by the controlateral suboccipital approach, in the plane of the ear-drum and in line with the general axis of the ossicules (author's transl)].

Definition and technique of the Dulac 7 incidence. Diagrams 1 and 2 give details of the anatomical orientations which define this incidence. It is:--centered on the head of the malleus,--orientated in the plane of the ossicules or in the neighbouring plane of the ear-drum,--parallel to the general axis of the ossicules,--close to the perpendicular to the tegment tympani. This incidence is easy to obtain with our technique, using a fixed intracranial centering point, The transversal linear scanning is very effective and can be completed in a very short period. It should be noted, however, that in obese subjects with short necks, the entry point of the incidence is difficult to obtain as there is interposition of the neck muscles. Under these conditions, one should try to be as close to this entry point as possible, knowing that the results are still valid. Tomographic anatomy. A close examination of the text of figures 6, 7, and 8 will familiarize the reader with the tomographic anatomy of this incidence. To summarize the important information obtained from the Dulac 7 incidence we should note that in tomographies of normal petrous bones:--the attic is always perfectly visible, expecially its internal and external walls throughout their total length, and more especially the anterior wall;--the ossicles (head of the malleus, body of the incus, and their articulation) are always perfectly visible and distinct;--the inferior processes of the malleus and incus are always visible;--the external wall of the attic is visible throughout its length, more especially the anterior and posterior portions;--the anterior and posterior contours of the external auditory canal are particularly well-defined. Finally, this incidence also gives clear images of the temporo-mandibular joint, the antral region, the superior canal, and the internal auditory canal. A large experience of this incidence is required before interpreting the image of the foramen ovale. Tomographic pathognomonic signs. The texts of figures 9 to 24 are sufficiently demonstrative of the richness of the pathological data obtained from this incidence, without needing to repeat them here. We would only add that the degree of calcification of the ossicles and the anterior wall of the attic can be precisely determined. This incidence, therefore, gives valuable information in almost all middle ear affections. It is also necessary in order to study the external auditory canal.