part_of part of part of anatomical structure anatomical system digestive system hematopoietic system bursa of Fabricius An epithelial and lymphoid organ that develops as a dorsal diverticulum of the proctodeal region of the cloaca in birds. The luminal (interior) surface of the bursa is plicated with as many as 15 primary and 7 secondary plicae or folds. These plicae have hundreds of bursal follicles containing follicle-associated epithelial cells, lymphocytes, macrophages, and plasma cells. Lymphoid stem cells migrate from the fetal liver to the bursa during ontogeny. In the bursa, these stem cells acquire the characteristics of mature, immunocompetent B cells[WP]. The bursa is an organ found in birds involved in B cell differentiation[GO]. SCTID:86689007 BTO:0001699 Wikipedia:Bursa_of_Fabricius MESH:D002060 GAID:1205 UBERON:0003903