Maxillary sinus membrane and nerve. Endoscope view of the mucous membrane from the upper part of the maxillary sinus, with the infraorbital nerve running behind it (upper frame). The sinuses are the spaces in the facial bones of the skull, and the maxillary sinuses are found in the upper jaw bones (maxillae). Richly vascular mucous membrane lines the sinuses (blood vessels can be seen here). The infraorbital nerve is a branch of the trigeminal nerve and provides sensory innervation of the lower eyelid, upper lip, and part of the nose.