Between the vestibular folds and the vocal folds, there is a deep, elliptical depression termed the sinus of the larynx. It extends upwards undermining the vestibular fold, and its mouth is narrower than its cavity. Under cover of the anterior part of the vestibular fold is a slit-like aperture. This leads into the saccule of the larynx – a small diverticulum which ascends between the vestibular fold and the lamina of the thyroid cartilage. The saccule is of variable extent, but, as a rule, it ends blindly at the level of the upper border of the thyroid cartilage. Large saccules and other laryngeal diverticula are characteristic of many apes and monkeys.