Final answer:
The trachea is the structure that extends from the larynx to the mediastinum, where it divides into the two main bronchi which lead into the lungs.
Step-by-step explanation:
The structure that extends from the larynx into the mediastinum and divides into two main bronchi is the trachea. After the larynx, air flows into the trachea, also commonly known as the windpipe, which is a long tube that descends into the chest area. Before entering the lungs, the trachea divides into the right and left bronchi. These bronchi are further supported by cartilage to prevent collapse and have mucous membranes to trap particles, with cilia pushing debris towards the throat for expulsion. The bronchial tree is a term referring to the conglomerate of these branching bronchi, which function as passageways for air to move into and out of each lung.