except for a small part. The allantois is provided with a 

 canal which goes to the urinary bladder of the embryo. The 

 umbilical sac lies outside the allantoic cavity; it is not 

 joined with the allantois; its stem is connected with the 

 umbilical cord; and both the free ends of the sac are 

 connected with the chorion. The chorion forms a closed cavity 

 around all the other parts and is composed of two layers, of 

 which the thicker external one is enveloped by the placenta 

 as a belt and is connected with the uterine wall. The internal 

 layer covers the allantois, and the amnion is covered with the 

 allantois. Figure 19 shows the transverse section through the 

 fetus. The scheme shows the topographic relationship of the 

 fetal membranes and their cavities. In explaining the drawing, 

 Bojanus wrote that he omitted the blood vessels and the 

 internal layer of the chorion to make it more clear. It is 

 not difficult to realize that Bojanus succeeded in delineating 

 very accurately the most important relationships between the 

 individual embryonic membranes and the organs. 



In 1817 and 1818 Bojanus published three reports on the 

 allantois and the umbilical sac in horses^ and sheep. 5 In the 

 first, he argued with Dutrochet, whose investigations Bojanus 

 saw as creating greater confusion than they eliminated. 

 Dutrochet indicated that the umbilical sac, with the fetus and 

 the amnion covering it, is included in the allantoic cavity. 

 He considered also that in the human fetus, as in the mare 

 fetus, the allantois fits closely to the entire internal 



4. L. Bojanus, "Allantoides und vesicula umbilicalis des 



Pf erdef oetus . Bemerkungen aus dem Gebiete der vergleichenden 

 Anatomie," RUSSISCHE SAMMLUNGEN FUR NATURWISS. U. 

 HEILKUNST, Riga u. Leipz., 2 (1817) preprinted in ISIS 

 (1818), pp. 1426 - 1427. L. Bojanus, "Uber die Darmblase 

 des Pf erdef oetus , " ISIS (1818), pp. 1633 - 1636. In this 

 last work a teaching scheme is included for the reciprocal 

 relationship of the embryonic membranes and organs, similar 

 to that given above for the dog embryo. 



5. L. Bojanus, "Uber die Darmblase des Schaafsf oetus, zum 

 Beweise, dass die vesicula umbilicalis mit dem Darm 

 unmittelbar zusammenhangt," ISIS (1818) , pp. 1623 - 1633; 

 also in Meckel's ARCH. ANAT . PHYSIOL. (1818). 



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