Developmental study on the facial nerve and canal in man (author's transl)

Abstract

The development of the facial nerve and its canal in the temporal bone was histologically investigated with serial sections in connection to the middle ear sugery.Materials used were 56 Japanese human embryos and fetuses aged from the 4th to the 23rd week (3.3 to 330mm in CR or CH length) that were stored in the Human Embryo Center for Teratological Studies of Kyoto University and Department of Otolaryngology, Okayama University Medical School. The results were as follows:1) The second arch epibranchial placode seemed to play an important role in the development of the geniculate ganglion.2) A trunk of the facial nerve, chorda tympani nerve and N. petrosus major accomplish before the ossicles appeared at the 6th week.3) The facial nerve was rapidly differentiated as the internal meatal, horizontal and vertical segments as with the development of the primordial stapes at the stage 17 and was gradually completed its normal running course by both the differentiation of the cartilagenous otic capsule and the pneumatization of the primitive tympanic cavity during the whole intra-uterine period.4) The development of the facial canal began as a sulcus on the canalicular division of the precartilagenous otic capsule at the stage 21. The formation of the tympanic boundary of the horizontal segment until the 22nd week of fetal life.5) Anson's hypothesis in which the head of malleus and the body of incus are made from Meckel's cartilage, and the handle of malleus and the long process of incus from Reichert's cartilage was supported.6) The rate of the thickness of the facial nerve to the diameter of the facial canal was large at the horizontal segment, but it was small at the vertical segment.