Thymus Gland

Thymus Gland, a gland which begins to form at an early period of embryonic life, and, commencing as an epithelial ingrowth from the throat, extends from the neck right into the chest, where it is placed anteriorly in the mediastinum. It continues to grow after birth, but when adult life is reached it shrivels to an inconsiderable mass. When examined microscopically it is seen to consist of a tissue very similar to that of a lymphatic gland, and in this tissue are (Hassall's corpuscles) nests of concentrically arranged epithelial cells, probably the remnants of that epithelium of which the gland, at an earlier period, was almost entirely composed. The gland when fully developed is what may be called a blood-gland, for it is connected with the rest of the system by blood-vessels and nerves alone, unlike the liver or kidneys, which are provided with ducts through which their secretion is carried away. Regarding the function of this gland almost nothing is known. It probably is concerned, in some way, in altering the chemical or cellular structure of the blood. Numerous extractives, such as lentin and tyrosin, are found normally in it, and from it a substance can be extracted which acts as a powerful blood coagulant. It is possible, too, that in its substance the blood-cells may to some extent be produced. Its early development and rapid disappearance suggest that its chief activity is called into play during that period of life when growth and tissue formation are most active.