The external branch of which nerve innervates the cricothyroid muscle?

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The cricothyroid muscle is innervated by the motor fibers of the external branch of the superior laryngeal nerve, a branch of the vagus. This branch courses with the superior laryngeal vessels and passes through the thyrohyoid membrane to reach the cricothyroid, where it provides the nerve supply that tilts the thyroid cartilage forward to tense the vocal cords and raise pitch. The internal branch of the superior laryngeal nerve, in contrast, supplies sensation to the laryngeal mucosa above the vocal cords, while the recurrent laryngeal nerve supplies all the other intrinsic laryngeal muscles (like the thyroarytenoid, interarytenoids, and vocalis) and below-the-fold sensation. The vagus is the parent nerve giving rise to these branches.