The thyroid gland is an endocrine organ of the body, located in the lower and middle part of the front of the neck. The thyroid gland is H-shaped and is divided into left and right lobes and a central thyroid isthmus. About half of the population has a cone-shaped lobe that extends upward from the isthmus and varies in length. Variations in the morphology of the thyroid gland often occur. The thyroid gland is wrapped by the pre-tracheal fascia, which forms the pseudo-peritoneum of the thyroid gland, the thyroid sheath. The outer membrane of the thyroid gland is called the true perithelium, or fibrous capsule. The gap between the two is the cystic sheath gap, which contains loose connective tissue, blood vessels, nerves, and parathyroid glands. The thyroid ligament formed by the thickening of the inner part of the pseudoperitoneum allows the thyroid gland to be attached to the thyroid cartilage, the cricoid cartilage and the tracheal cartilage ring behind both lobes and the isthmus, fixing the thyroid gland to the wall of the larynx and trachea. During swallowing, the thyroid gland moves up and down with the movement of the larynx. The blood supply to the thyroid gland is very rich, mainly from the superior thyroid artery (a branch of the external carotid artery) and the inferior thyroid artery (a branch of the subclavian artery), and occasionally from the inferiormost thyroid artery. There are extensive anastomotic branches between the branches of the superior and inferior thyroid arteries and between the branches of the superior and inferior thyroid arteries and the branches of the arteries of the pharynx, trachea and esophagus, so that during surgery, although all of the superior and inferior thyroid arteries are ligated, the residual part of the thyroid gland is still supplied with blood. The veins of the thyroid gland form a network in the body of the gland and then converge to form the superior, middle and inferior thyroid veins. The superior and middle veins merge into the internal jugular vein, and the inferior thyroid vein generally injects into the innominate vein. The lymphatic network in the thyroid gland is extremely rich and gradually concentrates under the thyroid envelope to form collecting ducts, which then lead out of the thyroid gland with or without peripheral veins and into the cervical lymph nodes. The lymph nodes in the neck are divided into seven zones: the first zone, the lymph nodes in the subchin and submandibular zones, bounded by the anterior belly of the diastasis muscle in the lower part and the mandible in the upper part; the second zone, the upper group of lymph nodes in the internal jugular vein, bounded by the posterior belly of the diastasis muscle in the upper part and the hyoid bone in the lower part, with the lateral border of the sternocleidomastoid muscle in the anterior part and the posterior border of the sternocleidomastoid muscle in the posterior part; the third zone, the middle group of lymph nodes in the internal jugular vein, from the level of the hyoid bone to the intersection of the inferior belly of the scapular hyoid muscle and the internal jugular vein The fourth zone, the inferior group of internal jugular vein lymph nodes, runs from the lower abdomen of the scapular hyoid muscle to the superior clavicle; the fifth zone, the posterior cervical triangle, is bounded posteriorly by the trapezius muscle, anteriorly by the posterior border of the sternocleidomastoid muscle, and inferiorly by the clavicle; the sixth zone (central group) ranges from the hyoid bone superiorly to the superior sternal hiatus and inferiorly to the internal border of the carotid sheath to the paratracheal and anterior trachea, including the cricothyroid lymph nodes, the tracheal and perithyroid lymph nodes, and the retropharyngeal lymph nodes Region VII, subsuperior sternal recess to anterior superior mediastinal lymph nodes. The nerves closely associated with the thyroid gland are the recurrent laryngeal nerve and the superior laryngeal nerve. The superior laryngeal nerve also comes from the vagus nerve and is divided into: the internal branch (sensory branch), which is located in the laryngeal mucosa; and the external branch (motor branch), which is close to the superior thyroid artery and travels with it, innervating the cricothyroid muscle and making the vocal cords tense. The superior laryngeal nerve is a branch of the vagus nerve, which travels down the lateral wall of the pharynx and divides into two branches at the large corner of the hyoid bone: the inner branch travels with the artery of the same name through the thyroid hyoid bone into the larynx and is distributed in the laryngeal mucosa above the vocal fissure and the epiglottis and tongue root; the outer branch travels with the superior thyroid artery to the front and below, and at a distance of 0.5 to 1.0 cm from the superior thyroid gland, it leaves the artery and bends medially to send out muscle branches to innervate the cricothyroid muscle and the subpharyngeal constriction muscle. Therefore, when ligating the superior thyroid artery during subtotal thyroidectomy, it should be performed close to the superior thyroid pole to avoid damaging the external branch of the superior laryngeal nerve and affecting pronunciation.