Abstract
In this study, we performed detailed examination of the terminal facial nerve branches to the mimetic muscles, particularly the branches terminating in the orbicularis oculi muscle and orbicularis oris muscle. Examination was performed on 20 Japanese adult autopsy cases, involving 20 hemi-faces. The mean age was 87.4 years (range: 60-99 years). There were 10 men and 10 women (10 left hemi-faces and 10 right hemi-faces). In each case, the facial nerve was exposed through a preauricular skin incision. The main trunk of the facial nerve was dissected from the stylomastoid foramen. A microscope was used to dissect and observe the terminal branches to the periphery. The temporal branch was distributed to the orbicularis oculi muscle in all cases and the marginal mandibular branch was distributed to the orbicularis oris muscle in all cases. The zygomatic branch was distributed to the orbicularis oculi muscle in all cases, but it was also distributed to the orbicularis oris muscle in 8 of 20 cases. The buccal branch was distributed to the orbicularis oculi muscle in 5 cases. There was no significant difference in the variations. According to textbooks, the temporal branch and zygomatic branch innervate the orbicularis oculi muscle, and the buccal branch (or the buccal branch and marginal mandibular branch) innervates the orbicularis oris muscle. In this study, we dissected the terminal facial nerve branches that terminate in the orbicularis oculi muscle and orbicularis oris muscle and examined their course and distribution in great detail. The results revealed multiple anomalies which are not described in conventional textbooks; these anomalies may compensate the movements of the muscles.
