Thyroid Gland

The Thyroid gland covers the trachea in front with its narrow isthmus at the level of the second through the fourth tracheal ring. The lower pole of each lobe lies lateral to the fifth and sixth tracheal rings. Since the right and left lobes incline posteriorly as they ascend the neck, the thyroid gland progressively overlaps more of the esophagus and pharynx and less of the trachea and larynx as the superior pole is approached. Each lobe is separated from the cricoid cartilage by the cricothyroid and the inferior pharyngeal constrictor muscles. The thyroid gland is separated from the thyroid lamina by the thyroid origin of the inferior pharyngeal constrictor. Each thyroid lobe is under cover of a sternothyroid muscle. The "organ packet," (larynx, trachea, pharynx, esophagus, and thyroid gland) always moves together during movements of swallowing.