The incisivii labii inferioris (lower) is the mandibular counterpart to the superior version, connecting the lower alveolus to the modiolus. Together with its superior counterpart it helps shape the lip corners during articulation.
| Origin | Alveolar process of the mandible — below the lateral incisor |
|---|---|
| Insertion | Modiolus at the lower lip corner |
| Nerve Supply | Facial nerve — marginal mandibular branch (VII) |
| Blood Supply | Inferior labial artery |
| Actions | Draws the lower lip corner medially during speech; Contributes to lower lip shaping |
|---|
The marginal mandibular branch innervation makes the inferior incisivii labii one of the muscles affected in marginal nerve palsy. In extensive mandibular surgery, both the incisivii labii muscles may be disrupted, contributing to post-operative lower lip asymmetry.
Not individually palpable — assessed as part of perioral muscle function.
Lower lip corner asymmetry from incisivii labii inferioris weakness after marginal mandibular nerve injury during neck dissection.
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