Lingula-when inspiring fully, the lingula of the left lung might partially fill the costomediastinal recess. the lingula, a tongue-like projection of the left lung below the cardiac notch, is right next to the costomediastinal recess. if the apex of the lung was highly inflated, it might expand to fill the cupola. the hilum is the part of the lung where the structures forming the root of the lung-the main bronchus, pulmonary vessels, bronchial vessels, lymphatics, and nerve-enter and leave the lung. it does not expand on inspiration. the middle lobe of the lung may expand to fill the costomediastinal recess, but remember that the question is specifically asking about a left lung structure, and the middle lobe is only in the right lung!