Which structure serves as a boundary for the nasal fossae?

The nasal septum serves as a boundary for the nasal fossae by dividing the nasal cavity into two symmetrical halves. Composed of both bone and cartilage, the septum is integral in providing structure and support to the nasal passages. It affects airflow and influences various functions, such as breathing, smell, and overall nasal health.

The other structures listed do not serve this specific boundary function. The genial tubercle is a bony prominence on the mandible where muscles attach and does not have any role in defining the nasal cavity's boundaries. The maxillary sinus is an air-filled space located near the nasal cavity, but it does not serve as a divider. The mandibular canal is a passageway within the mandible that houses the inferior alveolar nerve and blood vessels, also unrelated to the delineation of the nasal fossae.