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Fig. 308. Human embryo of 5 weeks

The ventral body wall has been removed to disclose the mesonephroi. (Kollmann)

The primary mesonephric tubules are arranged segmentally, one appearing in each segment as far back as the pelvic region. Thus the intermediate cell mass may be considered as a series of nephrotomes, corresponding to the sclerotomes and myotomes. The segmental character is soon lost, however, owing to the inequality of growth between the mesonephros and the other segmental structures, and to the development of the secondary and tertiary tubules. As stated above, the first mesonephric tubules appear immediately caudal to the pronephros From this point their formation gradually progresses in a caudal direction as far as the pelvic region. By the further development of the primary and by the addition of the secondary and tertiary tubules and the glomeruli, the mesonephros as a whole increases in size and forms a large structure which projects into the ccelom on each side of the body, forming the so-called mesonephric or Wolffian ridge. It reaches the height of its development in the human embryo about the fifth or sixth week, at which time it extends from the region of the heart to the pelvic region (Fig. 308). Each organ is attached to the dorsal body wall by a distinct mesentery which, at its cephalic end, also sends off a band to the diaphragm the diaphragmatic ligament of the mesonephros.

The peritoneum is reflected over the surface of the mesonephros, and on the ventro-medial side the mesothelium becomes thickened to form the genital ridge (Figs. 276 and 308).


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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)

Reference

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



Cite this page: Hill, M.A. (2019, March 26) Embryology Bailey308.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bailey308.jpg

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