C

Reasoning: In the standard cortical mastoidectomy view, the lateral (horizontal) semicircular canal appears as a distinct bony prominence situated superior-posterior to the horizontal segment of the facial nerve and just anterior to the sigmoid sinus. In commonly used teaching diagrams, this landmark is consistently denoted by arrow “C” [Ulug 1998, PMID 9871399; Wanibuchi 2022, PMID 35670164].