In submandibular surgery incision is given 2 cm below the border of mandible to preserve which nerve?

The mandibular branches of the facial nerve run parallel to the lower border of the mandible, mostly below it. Of them, the marginal mandibular nerve follows almost exactly the lower border. Hence, to avoid sectioning of this nerve and causing loss of motor supply to lower lip and mentalis, we give the submandibular incision at lest 2 cm of 2-finger width below the lower border of mandible.