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 *coid, just above the sternal notch, incision being made through the cartilage.

—The upper thorax of a child eight years old, showing the thyroid and thymus glands. (Sobotta.)

Extending up on either side of the upper trachea in the neck are the two lobes of the thyroid gland, the isthmus, which connects the lobes, covering the trachea below anteriorly. The function of the gland is obscure, but it has an internal secretion of great importance in the metabolic processes. Its removal or disease is followed by general disturbances of mind and body. The injection of thyroid extract has proved effective as treatment. In goiter the gland becomes enlarged. The thymus gland lies below the thyroid gland at birth, in front of and at the sides of the trachea, and runs down behind the sternum. It is largest at the end of the second year, after which it atrophies, being almost absent at puberty. It, too, is ductless and its function is not well understood.