Thyroid & Parathyroid Gland Surgical Anatomy — Practice

A 58-year-old woman undergoes a thyroidectomy for a multinodular goitre. Postoperatively she develops a hoarse, breathy voice and on indirect laryngoscopy the affected vocal cord lies in the paramedian position. The surgeon notes the injured nerve had been closely related to the inferior thyroid artery near the gland. Which laryngeal muscle's paralysis chiefly accounts for her inability to abduct the vocal cord?