Final answer:
The cricothyroid ligament bifurcates at the superior border of the thyroid cartilage and regulates the tension on the vocal folds.
Step-by-step explanation:
The structure that bifurcates at the superior border of the thyroid cartilage is the cricothyroid ligament. It is a connective tissue that attaches the thyroid cartilage to the cricoid cartilage, which forms part of the larynx. This ligament helps to regulate the tension on the vocal folds, enabling changes in pitch during speech.