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Fig. 292. From a model of the septum transversum and liver of a human embryo of 3 mm

His, Kollmann.

The communication between the pericardial cavity and the rest of the embryonic ccelom is soon partly cut off by the development of a transverse fold - the septum transversum. This septum is formed in close relation with the omphalomesenteric veins. These vessels unite in the sinus venosus at the caudal end of the heart, whence they diverge in the splanchnic mesoderm. They are thus embedded in the mesodermal layer of the splanchnopleure, and as the latter closes in from either side to form the gut, the vessels form ridge-like projections into the ccelom. As the vessels increase in size, the ridges become so large that the splanchnic mesoderm is pushed outward against the parietal mesoderm and fuses with it (Fig. 291). Thus a partition is formed on each side, which is attached on the one hand to the mesentery and on the other hand to the ventral and lateral body walls, and which contains the omphalomesenteric veins. It is obvious that these partitions, forming the septum transversum, close the ventral part of the communication between the pericardial cavity and the rest of the ccelom. The dorsal part of the communication remains open on each side of the mesentery as the ductus pleuro-pericardiacus (dorsal parietal recess of His) (Figs. Fig. 291 and Fig. 292).

As the heart develops it migrates caudally, and by corresponding migration the pericardial cavity draws the ventral edge of the septum transversum farther caudally, so that the cephalic surface of the latter faces ventrally and cranially.

In other words the septum comes to lie in an oblique cranio-caudal plane. The pericardial cavity therefore comes to lie ventral to the ductus pleuro-pericardiaci. The latter one on each side of the mesentery are two passages which communicate on the one hand with the pericardial cavity and on the other hand with the peritoneal cavity, while they themselves form the cavities into which the lungs grow the pleural cavities. (Compare Figs. Fig. 292, Fig. 293 and Fig. 294.)


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Reference

Bailey FR. and Miller AM. Text-Book of Embryology (1921) New York: William Wood and Co.



Cite this page: Hill, M.A. (2019, January 19) Embryology Bailey292.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bailey292.jpg

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