. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 512^ mesoblast has throughout split into two layers, the coelomic cavity has appeared not only in the embryo proper but in the extra-embry- onic part of the blastoderm. A fold of .the somatic mesoblast enclos- ing a part of the coelomic cavity now insinuates itself on each side into the hitherto solid epiblastic amniotic fold of the dorsal region, dividing the latter into two limbs: the inner amnion proper and the outer serous envelope. In the mid-dorsal line, the two mesoblastic folds almost come together but do not touch ea
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 512^ mesoblast has throughout split into two layers, the coelomic cavity has appeared not only in the embryo proper but in the extra-embry- onic part of the blastoderm. A fold of .the somatic mesoblast enclos- ing a part of the coelomic cavity now insinuates itself on each side into the hitherto solid epiblastic amniotic fold of the dorsal region, dividing the latter into two limbs: the inner amnion proper and the outer serous envelope. In the mid-dorsal line, the two mesoblastic folds almost come together but do not touch each other as a string of cells connects the serous envelope and the amnion, and separates the extra-embryonic coelomic cavities of the two moieties of amnion (Diag. IIP). In the head region, the coelomic cavities become early united across (Diag. III). 6. One of the most important results of the present investigation is in reference to this connection between the amnion and the serous envelope. Contrary to what is hitherto known, the extra- embryonic coelomic cavities of the two moieties of the amnion are never united across with each other over the dorsal region of the embryo. A connection — quite elongated and definite in later stages — between the amnion and the serous envelope separates them to the very end of the development. This structure causes great peculiarities in the foetal membranes in later stages. This connection I propose to call the sero- am niotic connection. It does not extend into the region of the sunken head where the amnion originally consisted of the hypoblast and epiblast. 7. The most remarkable part in the history of the amnion is the following fact: the anterior and lateral iolds which starting from the head have gradually extended backward over the whole em- bryo, do not stop at the posterior end of the embryo but continue to grow backward, although diminished in its width, until finally there is produced a tube m ur. Please note that these images
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