The development of the branchial region in vertebrates is no less dependent on the cooperation of parts of different origin than is the mouth region. The leading part in the development of this area belongs to the endoderm. The endodermal cavity in this region, from its beginning, is distended in a transverse direction. In amphibians it is derived from the [...]
In this article we will discuss about:- 1. The Lungs in the Vertebrates 2. The Liver in Vertebrates 3. The Pancreas and Bursa Fabricii in Vertebrates. The Lungs in the Vertebrates: The lungs develop from a rudiment which is a pocket-like evagination of the endodermal epithelium on the ventral side of the alimentary canal, just posterior to the branchial region. [...]
Experimental investigation of the endoderm in early stages of development shows that the endodermal organ rudiments, like those derived from other germinal layers, are not initially determined, but that the endodermal cells destined to participate in the formation of the various organ rudiments are no more determined for their respective fates than are the cells of the other germinal layers. [...]