In birds, the bone marrow is the site of hematopoiesis and the bursa of Fabricius (Latin: Bursa cloacalis or Bursa fabricii) is a specialized organ that, as first demonstrated by Bruce Glick and later by Max Cooper and Robert Good, is necessary for B cell development. Mammals generally do not have an equivalent organ; the bone marrow is often both the site of hematopoesis and B cell development. Orders Many - see section below. ... Bone marrow (or medulla ossea) is the tissue comprising the center of large bones. ... Haematopoiesis is the formation of blood cellular components. ... Latin is an Indo-European language originally spoken in the region around Rome called Latium. ... In biology, an organ (Latin: organum, instrument, tool) is a group of tissues, which perform a specific function or group of functions. ... Orders Subclass Multituberculata (extinct) Plagiaulacida Cimolodonta Subclass Palaeoryctoides (extinct) Subclass Triconodonta (extinct) Subclass Placentalia Afrosoricida Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Litopterna (extinct) Macroscelidea Mesonychia (extinct) Notoungulata (extinct) Perissodactyla Pholidota Plesiadapiformes (extinct) Primates Proboscidea Rodentia Scandentia Sirenia Taeniodonta...

The ‘B’ in ‘B cell’ refers to bursa-derived. This is simply because during the 1960s B cells were first defined (and distinguished from thymus-derived T cells) in birds, which have a bursa. A decade later, after examining almost every other organ including the appendix, researchers finally discovered that mammalian B cells develop in the bone marrow. The fact that ‘bone marrow’, like bursa, starts with a ‘B’ is a (fortunate?) coincidence.