Thyroid: A gland located beneath the larynx (voice box) that makes thyroid hormone and calcitonin. The thyroid helps regulate growth and metabolism.The thyroid gland consists of two lateral lobes united by a strip of glandular tissue called the isthmus. It is covered by two capsules: an inner capsule of fibroelastic tissue and an outer capsule continuous with and part of the deep cervical fascia. The main physiological action of the thyroid is to assist in regulating the metabolic rate in concert with growth and tissue regulation. The lymph nodes are: delphian node, anterior cervical (prelaryngeal, pretracheal, laterotracheal [recurrent laryngeal nerve chain]), internal jugular (jugulodigastric and jugulo-omohyoid), tracheoesophageal, mediastinal (upper anterior and posterior [tracheoesophageal]), and retropharyngeal.