IN THE anatomic and otologic textbooks the course of the descendant part of the facial nerve is stated to be constant, and during an operation it may be localized simply by running a straight line from the most overhanging point of the lateral semicircular canal to the stylomastoid foramen. Bridgett1proceeds in the following manner: A probe inserted into the mastoid notch will point directly toward the stylomastoid foramen; after the exenteration of the cells in the tip of the mastoid process, however, this notch can be seen as a salient ridge, the crista digastrica at the floor of the cavity. If this ridge is followed anteriorly as far as the posterior wall of the acoustic meatus it will be seen to end at the stylomastoid foramen, from which a thin, bony lamina passes upward, toward the lateral semicircular canal, indicating the course of the nerve. The intersecting point of