Abstract:
Background. The data reported in the specialty literature on the embryogenesis of the facial nerve mainly refer to the
initial stages of its development. Nevertheless, the intrauterine development of the facial nerve is a complex and insightful
process, characterized by a range of peculiarities. The goal of our study was to highlight the specific developmental features
of the facial nerve for a better understanding of its morphology in adults.
Material and methods. Fifty-two groups of serially sectioned human embryos and fetuses from the embryo-fetal collection
of the Department of Normal Anatomy at the Belarusian State Medical University in Minsk were investigated. The
embryonic samples were classified according to Carnegie stages (day of gestation and crown-rump length). For protocols
description, an OLYMPUS CX31 binocular microscope (eyepiece 10x, objectives 4x; 10x; 40x; 100x) and a Nikon DS-Fi1
camera were used.
Results. The primary and secondary divisions of the facial nerve trunk, the chorda tympani, the greater petrosal nerve, and
the intracerebral and peripheral connections of the facial nerve were distinguished at Carnegie stage 15. The first appearance
of intraplexal connections within the parotid plexus was identified at Carnegie stage 16. At stage 20, thin connections
between the geniculate ganglion and the vestibular ganglion were revealed. Macro- and microstructural changes in the
geniculate ganglion were noted throughout its development. The plexiform nature of the peripheral divisions of the facial
nerve and the formation of the pes anserinus minor were observed at stage 21. At Carnegie stage 23, the motor nucleus was
well developed, and the internal knee of the facial nerve was identified.
Conclusions. Early specific features of facial nerve development include: 1) intracerebral and peripheral connections with
neighboring cranial nerves; 2) intraplexal connections between branches of the parotid plexus; 3) distinguishable intracerebral
pathways; 4) connections between the geniculate and vestibular ganglia. Late developmental peculiarities include:
1) progressive macro- and microstructural changes in the geniculate ganglion; 2) appearance of the pes anserinus minor;
3) formation of the motor nucleus, internal knee, and intracerebral pathways. These specific developmental features of the
facial nerve provide clear evidence of its complex morphology in adults.
