THYROID GLAND, a structure having no outlet or duct, and classified with the spleen, thymus gland and suprarenal capsules under the general name of ductless glands. In man the thyroid gland is situated at the upper part of the trachea or windpipe and consists of two halves or lobes, placed one on each side of the windpipe, and united by a narrow bridge of substanceó the isthmus of the gland. It is covered in front by the muscles of the nedr and its sides lie in contact with the common carotid artery. Its ander surfaces embrace the windpipe and larynx. This gland is of a red dish color. It is larger in women than in men, and weighs, on an average, about one and one half ounces. It may become enormously en larged, as in goitre. Its structure consists of numerous small shut sacs, surrounded by a net work of capillary blood-vessels. Each vesicle or shut sac is lined internally by a single layer of columnar cells, and is filled with a glairy mucoid substance. The blood-vessels of the
gland are derived from the superior and in ferior thyroid arteries and its nerves come from the pneumogastric and sympathetic trunks. The use of this gland is not quite clear, but is gen erally held to be the production of a secretion which has a great influence on alimentation. Its business is connected with the maintenance of a proper quality of blood, either by the re moval of certain effete substances from the blood, or by the addition of certain elements to it Its complete estimation or atrophy is attended with disease. The thyroid gland of the sheep is used in the treatment of myxce dema, the complication resulting from the loss of function of the gland.