This is found in the lower part of the neck, in the upper part of the thoracic cavity. It is fairly large at birth, and increases in relative size up until late childhood. After the age of puberty it gradually becomes smaller, until it virtually shrinks into oblivion.
Some important types of white blood cells are manufactured there and it obviously plays an important role in early life in helping to protect the system. However the full extent of its functions still remains something of a mystery. It seems to play a part in a disease of later life called myasthenia gravis in which the muscles tire rapidly. Sometimes if the thymus gland is removed, recovery occurs, but on the other hand if this happens, the person can sometimes develop another sinister disease called systemic lupus erythematosus.
Tumors can grow in the Thymus gland, and aggravate the symptoms of myasthenia gravis. Cysts and other lumps may occur, but these are fairly rare. If there is a tumor it is removed surgically, for fear that it might become cancerous.