Labyrinthine segment and geniculate ganglion of facial nerve in fetal and adult human temporal bones.

The later stages of development (15-40 weeks in utero) of the geniculate ganglion and labyrinthine segment of the facial nerve in the human fetus demonstrate minimal neuronal growth. The vascular supply is well established. The major changes occur in the perineural ossification pattern. The canal of the labyrinthine facial nerve segment ossifies first via the petrous apex and periotic capsule. The narrowest portion of the canal is at the geniculate ganglion in the earlier stages and at the fundus of the internal auditory canal at term. The geniculate ganglion area ossifies by means of two bony plates. The medial plate is a derivate of the periosteal growth of the petrous apex and the lateral plate is an extension of membranous bone from the squama. The major relationships to the middle ear do not change. The hiatus of the facial canal diminishes in size during gestation, but remains patent at birth.