III The Development of the Facial Nerve in Man

Abstract

This paper presents the morphogenesis of the intracranial and extracranial parts of the facial nerve in human embryos. Included are the development of the roots, the geniculate ganglion, the branches, the interanastomoses and the anastomoses between the facial and other nerves in the head and neck regions. The facial nerve develops from the facioacoustic primordium of the 2nd branchial of hyoid arch (4. 2 to 8. 0 mm) in close proximity to the placode of the arch. The facial division of the primordium separates from the acoustic division by 8. 0 to 10. 6 mm and develops a geniculate ganglion that becomes evident as the placode disappears. The chorda tympani and the greater petrosal nerves are the first branches to form followed by the posterior auricular and posterior digastric nerves. The facial nerve terminates peripherally in early embryos as a loose network of intermingling fibers. By 14 to 20 mm the nervus intermedius can be recognized, the chorda tympani joins with the lingual nerve and connections are made between the facial nerve and the branches of the 2nd and the 3rd cervical ganglia. The terminal branches of the facial nerve course into occipital, cervical, mandibular and infraorbital regions. The muscular branches of the facial nerve follow pari passu the formation of the facial muscle masses and, in most cases, develop deep to them. The peripheral divisions of the facial nerve are present at 26 mm and communications exist with infraorbital, buccal, auriculotemporal and mental branches of the trigeminal nerve. All of the common communications between the branches of the facial and of other nerves are formed by 80 mm with the exception of the zygomaticofacial, lacrimal, infratrochlear and external nasal branches of the trigeminal nerve which are present at 146 mm. Branches of the 2nd and the 3rd cervical ganglia, which communicate early with the facial nerve, become established later as the great auricular, the transverse cervical and the lesser occipital nerves.