Anatomical localisation of the marginal mandibular branch of the facial nerve.

The marginal mandibular nerve was studied post mortem in 50 human subjects. The nerve was found to be presented by one branch (32%), two branches (40%) and three branches (28%). The relationship of the nerve to the lower border of the mandible was variable: it was either totally above the lower border of the mandible (28%), below the mandible (44%) or in 28% of cases lying above and below it. The branch which lay below the lower border of the mandible crossed it opposite the masseter muscle or opposite the facial artery or else anterior to the facial artery. The branches which lay above the lower border of the mandible were always deep into the superficial layer of the parotid fascia, while below the mandible all the branches ran intrafascially. The termination of the nerve was always deep to the muscles of the lower lip. The results of the present study were discussed and correlated with the results of other authors from the anatomical and surgical points of view. It is concluded that the lower border of the mandible can serve as an important landmark to help avoid injury to the nerve; above it a subplatysmal flap is satisfactory but below it a subfascial flap is much safer.