File:Bailey305.jpg

Fig. 305. Transverse section of a dog embryo with 19 primitive segments

Bonnet.

• Section taken through sixth segment.
• The pronephric tubules are but transient structures and have no functional significance in man and the higher Vertebrates.
• The ducts, however, remain and become the ducts of the second set of urinary organs, the mesonephroi.
• primitive segments = somites.

The pronephros, with the pronephric duct, is the first of the urinary organs to appear. In embryos of 2-3 mm. there are two pronephric tubules on each side, situated at the level of the heart. Although their mode of origin has not been observed in the human embryo, it is probable, judging from observations on lower Vertebrates, that they arise as evaginations of the mesothelium. The part of the mesothelium involved is that adjacent to the intermediate cell mass (Fig. 305) .

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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. (2024, April 23) Embryology Bailey305.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bailey305.jpg

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