Final answer:
The thyroid cartilage serves as an important visual landmark when performing endotracheal intubation under direct visualization, recognized by its prominence known as the "Adam's apple."
Step-by-step explanation:
When performing endotracheal intubation under direct visualization, an important visual landmark is the thyroid cartilage of the larynx. This structure is often recognized by its prominence, known colloquially as the "Adam's apple." The thyroid cartilage is anterior to the larynx, and its identification is crucial in guiding the placement of the endotracheal tube. In the context of laryngeal anatomy, the epiglottis, vocal cords, and cricoid cartilage are also relevant landmarks during intubation. Among the options provided, the cricoid cartilage is also important because it forms a complete ring around the trachea and serves as a site below which the endotracheal tube is passed during intubation.