part_of part of part of has developmental contribution from has developmental contribution from primordium immune system pharyngeal gland pharyngeal epithelium vagal neural crest thymus primordium uberon thymic rudiment EMAPA:17523 EFO:0003622 A small outgrowth of the pharyngeal epithelium that is the site of lymphocyte cell production[ZFA]. [PMID]. TAO:0001077 thymic primordium UBERON:0005562 EHDAA:2969 A small outgrowth of the pharyngeal epithelium that is the site of lymphocyte cell production. Willett et al, 1999.[TAO] we follow Kardong table 13.1 in having some developmental contribution of pouch 4 in mammals, but this isn't reflected in EHDAA2. Consider adding distinct term for mesenchyme (see EHDAA2), to indicate NC constribution. variability of developmental origin: In fish, thymic primordia are generated by all the pouches except the first. However, in avians the thymus arises from pouches 3 and 4, whereas in humans it is only generated by the third pouch[PMID:16313389] The thymus arises from the second pouch in frogs, 2-6 in cartilaginous fish, 2-3 in reptiles, 3 or 4 in bony fish, birds and mammals. The final number is variable - 5 paired organs in sharks, 4 in caecilians, 3 in urodeles, 1 in many teleost, anurans and many mammals EHDAA2:0002023 ZFA:0001077