Lung fusion with the liver in chick and quail embryos

Abstract

The diaphragm separates the lung and liver in adult mammals.However, in human embryos before development of the muscular diaphragm, the lung faces the liver with a separation by the thin pleura and narrow pleural cavity: thus, a mesothelium-to-mesothelium attachment is likely (Cai et al., 2020;Hayashi et al., 2011;Jin et al., 2020). In adult birds, instead of the muscular diaphragm, the costopleuralis muscle (striated muscle; analogy of the subcostalis in mammals) separates the posteriorly restricted lung from the liver (DeWet et al., 1967). The costopleuralis muscle contributes onto the respiratory movement in birds. The abdominal air sac (bilateral structures connecting to the lung) as well as the pleuroperitoneal muscle seems to separate the dorsally located lung from the liver in the adult domestic fowl. However, the anatomy of the covering pleura and peritoneum is not shown even in an excellent atlas by Yasuda (2002).Although textbooks of human embryology (e.g., Hamilton & Mossman, 1972;O'Rahilly & Müller, 1996) did not state, in embryos