The '''Thymus''' is a ductless two-lobed [[gland]] lying behind the breast bone and composed mainly of [[lymphoid]] [[cells]]. It plays a part in setting up the body's [[immunity system]]. After [[puberty]], it declines in size. | The '''Thymus''' is a ductless two-lobed [[gland]] lying behind the breast bone and composed mainly of [[lymphoid]] [[cells]]. It plays a part in setting up the body's [[immunity system]]. After [[puberty]], it declines in size. |