Fig. 2. A. Schematic showing positioning for a Waters projection. (CM, canthomeatal line; CR, central ray) B. Radiograph of a Waters projection. The petrous ridge lies below the maxillary sinus. (a, frontal sinus; b, medial orbital wall; c, innominate line; d, inferior orbital rim; e, orbital floor; f, maxillary antrum; g, superior orbital fissure; h, zygomatic-frontal suture; i, zygomatic arch) (A; Rao VM, Gonzalez CF: Plain film radiography and polytomography of the orbit. In Gonzalez CF, Becker MH, Flanagan JC [eds]: Diagnostic Imaging in Ophthalmology, pp 1–7. New York, Springer Verlag, 1986)