Abstract
The diameter and course of the Chorda tympani were studied in 35 human embryos aged 4 to 24-weeks. Serial paraffin sections were cut and then observed under a light microscope. For comparison, the adult Chorda tympani was also examined.
The chorda tympani could be identified in 5-week embryos. In one of these 5-week embryos, the diameter of the facial nerve was 68.1 em and the diameter of the chorda tympani was 59.8μcm. This indicates that the chorda tympani occupied the majority of the facial nerve. Thereafter, the development of the chorda tympani and facial nerve proceed indepedently. The diameter of the chorda tympani developed from 60 pm (5-week embryo, 1 ear) to 235μm (24-week embryo, 1 ear), whereas the facial nerve grew from 87μm (4-week embryo, 2 of average ears) to 446μm (24-week embryo, 1 ear). The diameter ratio (chorda tympani/facial nerve) was larger (40%) in embryos (from 5-weeks to 24-weeks except for 17-weeks) than in adults (22.3%).
In embryos (from 5 to 8-weeks), the angle of the chorda tympani branch splitting off from the facial nerve was wider [79.6 (7-weeks)-112 (8-weeks) degrees] than in adults (25.2 degrees).
In adults, the number of fibers in the chorda tympani was 1555 (average of 4 ears) and the facial nerve had 7863 fibers (average of 3 ears).
