The diagnosis of tumors in the cerebello-pontile angle or of tic douloureux, as a rule, does not offer much difficulty, but that a tumor of the cerebello-pontile angle should be diagnosed as tic douloureux for six years is somewhat remarkable. In spite of numerous operations, including removal of the ganglion and cutting of the sensory root, the pains persisted and were considered functional. The mistake in the diagnosis was due to the failure of recognition that the pains were the result of irritation of the roots of the glossopharyngeus. The case offered opportunity for physiologic study of the functions of the ninth and twelfth cranial nerves. REPORT OF CASE CLINICAL HISTORY The patient, T., aged 35, a man with negative family and personal history, in 1903 first began to have pain in the right upper teeth, for which he consulted a dentist. A tooth was extracted, but the pain continued