392 PRACTICAL AN ATOM r. 



THE THYMUS GLAND. 



The tliymus gland, with the thyroid, supra-renal cap- 

 sules, and spleen, belongs to the ductless glands; it attains 

 its greatest development about the second year, when it 

 begins to atrophy, and, by the sixteenth year, has 

 entirely disappeared ; it consists of two lobes, situated 

 in the anterior mediastinum, extending as low as the 

 fourth costal cartilage ; it is pink in color and lobulated, 

 and weighs, when bestd eveloped, about an ounce ; the 

 lobes are formed of lobules, which present a cellular, 

 cortical, and medullary portion ; it is essentially a gland 

 formed of lymphoid elements, and is probably concerned 

 in the formation of red blood-corpuscles. 



