Write in details about Thymus.

Thymus is a lobed organ located near the heart and beneath the breastbone.

Thymus is quite large at the time of birth but keeps reducing in size with age and by the time of puberty is attained it reduces to a very small size.

Both bone marrow and thymus provide micro environment for the development and maturation of $T$-lymphocytes.

The stem cells of the bone marrow which gives rise to $T$-lymphocytes must pass through the tissue of thymus gland before they become fully functional.

In thymus they develop into cells called Thymocytes. Some of the Thymocytes mature into $T$-cells.

They leave the thymus gland and enter the blood stream. Some stay in the blood and some migrate to the tissue fluid, lymph nodes and other organs such as spleen