Excerpt from The American Journal of Anatomy, 1912, Vol. 12 Born's article reviews the earlier development of the cloa eal region in a very complete manner, and the substance is as follows: The entoderm of the enteron comes into direct relation with the surface ectoderm in the pharyngeal and cloacal membranes during the formation of the head and tail folds. Both of these membranes lose their primitive position and become folded into the substance of the embryo through increase in the surrounding mesoderm. The allantois, which is developed dorsally in the mammalian embryo (human and guinea pig excepted), shifts to a ventral position on the gut, and is gradually displaced from its intimate relation to the yolk sac through increase in the amount of mesodermal tissue. The primitive streak is carried to the ven tral surface of the body during the formation of the tail fold, and forms the whole or part of the cloacal membrane. Kolliker Strahl and Bonnet believe that the caudal end of the primitive streak is made up of applied layers of ecto and entoderm, and that it enters as such into the formation of the cloacal membrane. Keibel argues that this primitive rela tion of the ecto and entoderm is lost through interposition of mesoderm; the latter disappearing later with restoration of the original two layered condition. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.