Bursa of Fabricius

**Definition:** An epithelial outgrowth of the cloaca in birds similar to the thymus in mammals. It atrophies within 6 months after birth and remains as a fibrous remnant in adult birds. It is composed of lymphoid tissue and prior to involution, is the site of B-lymphocyte maturation.

**Tree numbers:** - A10.549.175 - A13.163 - A15.382.520.604.114