What structure separates the two cavities of the nose?

The nasal septum is the structure that separates the two cavities of the nose. It is composed of bone and cartilage and runs vertically down the center of the nasal cavity, dividing it into the left and right nasal passages. This division is essential for proper airflow and function of the respiratory system, allowing each side to filter, warm, and humidify the air that enters the lungs.

The nasal cavity refers to the entire space inside the nose but does not specifically highlight the dividing structure. The pharynx is located further down and serves as a passageway for both air and food but is not involved in separating the nasal cavities. The larynx, commonly known as the voice box, is also situated below the nasal cavity and does not play a role in the separation of the nasal cavities. The nasal septum's role is fundamental, making it the correct answer.