Book - Aids to Embryology (1948) 11

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Baxter JS. Aids to Embryology. (1948) 4th Edition, Bailliere, Tindall And Cox, London.

Contents: 1. Germ Cells | 2. Segmentation and Germ Layer Formation | 3. Changes in Female Genital Tract | 4. Implantation and Placentation | 5. Formation of the Embryo | 6. Skin and Accessory Structures | 7. Nervous System | 8. Special Sense | 9. Alimentary Canal | 10. Circulatory System | 11. Coelomic Cavities | 12. Urogenital System | 13. Muscular and Skeletal Systems | 14. Hereditary
Historic Disclaimer - information about historic embryology pages 
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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Chapter XI The Coelomic Cavities

The primitive ccelomic cavity is formed by the confluence of spaces which arise in the lateral plate mesoderm on each side of the embryonic disc (p. 19). Anteriorly, the two cavities thus formed communicate with each other across the mid-line in the region of the cardiogenic plate so that the early coelom is horseshoe-shaped. It becomes subdivided into pericardial, pleural, and peritoneal cavities by the formation of a transversely placed mass of mesoderm known as the septum transversum, and also by certain changes associated with growth of the heart and lungs.


The Pericardial Cavity

When the developing heart becomes folded under the foregut, the anterior part of the coelom, from whose roof it is now suspended by the dorsal mesocardium, occupies a position at right angles to the remainder of the body cavity and is limited caudally by the septum transversum. This caudal boundary is not complete, for on each side there is a dorso-lateral communication, the pleuro-peritoneal canal. The free dorsal edges of the septum bounding this in front contain the common cardinal veins. The lung buds now appear and bulge caudo-laterally into the upper part of each pleuro-peritoneal canal, which may now be regarded as the primitive pleural cavity. The heart undergoes a descent relative to the surrounding structures and so the common cardinal veins are forced to run in an increasingly oblique direction caudomedially to reach the sinus venosus. Each vein raises up a ridge whose free border is directed inwards. These are the pleuro-pericardial folds, and their free edges eventually fuse with the mesoderm ventral to the oesophagus, so closing off the pericardial cavity from the rest of the coelom. These pleuro-pericardial walls now become differentiated into pleural membranes externally and parietal serous pericardial membranes internally. The mesodermal tissue on the outer surface of the latter forms the fibrous pericardium. The visceral layer of the serous pericardium is formed from the most superficial tissue of the original myo-epicardial mantle. The oblique sinus of the pericardium arises as a result of changes in the atria when the sinus venosus and the pulmonary veins become incorporated in these chambers. The transverse sinus of the pericardium marks the site of breakdown of the original dorsal mesocardium (p. ioo).



Fig. 33. - Figures to show the Development of the Pericardial Cavity.

1, Spinal cord ; 2, notochord ; 3, pharynx ; 4, pleuro-pericardial recess ; 5, heart tube ; 6, pleuro-pericardial folds ; 7, pleuroperitoneal recess ; 8, pericardial cavity ; 9, lung bud ; 10, fibrous pericardium.


Formation of the Pleural Cavities and Diaphragm

The developing lung bulges into the primitive pleural cavity from the medial wall. With continued growth it scoops out for itself a secondary pleural cavity from the body wall tissue dorsal and caudal to the pleuro-pericardial membrane. This secondary cavity is limited caudally by a fold, the pleuro-peritoneal membrane, running from the posterior edge of the septum transversum upwards and backw r ards to the upper pole of the mesonephros. With further growth of the lung the dorsal end of the pleuro-peritoneal membrane is displaced caudally, and the lung also insinuates itself from behind on to the lateral aspect of the common cardinal vein and the phrenic nerve in the pleuro-pericardial membrane. Eventually in the eighth week the free medial edge of the pleuro-peritoneal membrane fuses with the mesoderm on the low r er part of the oesophagus and the pleural is closed off from the peritoneal cavity.

The diaphragm is made up of the following components :

  1. The cephalic layer of the septum transversum.
  2. The paired pleuro-peritoneal membranes. These become invaded by muscle cells from the third, fourth and fifth cervical segments during caudal migration.
  3. The oesophageal mesentery.
  4. Tissue derived from the body wall by the continued excavation of the pleural cavity into it.


Sometimes closure of the pleuro-peritoneal canal does not take place, allowing thus herniation of abdominal viscera into the pleural cavity. This is much more frequent on the left side than on the right.



Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)
Contents: 1. Germ Cells | 2. Segmentation and Germ Layer Formation | 3. Changes in Female Genital Tract | 4. Implantation and Placentation | 5. Formation of the Embryo | 6. Skin and Accessory Structures | 7. Nervous System | 8. Special Sense | 9. Alimentary Canal | 10. Circulatory System | 11. Coelomic Cavities | 12. Urogenital System | 13. Muscular and Skeletal Systems | 14. Hereditary

Cite this page: Hill, M.A. (2019, September 20) Embryology Book - Aids to Embryology (1948) 11. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Aids_to_Embryology_(1948)_11

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