Ectopic pulmonary cartilage and bone in domestic fowl

The occurrence and histological appearance of ectopic pulmonary cartilage and bone in domestic fowl was investigated. Its incidence was shown to vary in different strains of birds. The structures may occur in newly hatched chicks and are similarly present in birds maintained on diets containing bonemeal and diets without it. They could not be experimentally induced by bronchial insufflation of fine bone particles. Previous theories of their genesis are discussed and it is concluded that they do not originate from either inhaled dietary bonemeal or disease processes but are probably abnormal embryonic induction of mesenchyme or cartilaginous germ cells displaced from adjacent bronchi.