. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. DEVELOPMENT OF THE KIDNEY AND URETER. 233 maintaining that they come from the mesothelium of the body-cavity, while others believe that they are of ectodermic origin. Further changes bring about the hollowing out of the cell-cords so that there results a long tube, the pronephric or segmental duct, which has several short transverse tubulea —in some vertebrates, six ; in man, two—opening into it and communicating by their opposite open extremities, the neph- ridial funnels or nephrostomata, with
. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. DEVELOPMENT OF THE KIDNEY AND URETER. 233 maintaining that they come from the mesothelium of the body-cavity, while others believe that they are of ectodermic origin. Further changes bring about the hollowing out of the cell-cords so that there results a long tube, the pronephric or segmental duct, which has several short transverse tubulea —in some vertebrates, six ; in man, two—opening into it and communicating by their opposite open extremities, the neph- ridial funnels or nephrostomata, with the ccelom (Fig. 117). In the human embryo the pronephric tubules have been found with open nephridial funnels, but without connection with the pronephric duct. The mesothelium in immediate proximity to the open end of each short tubule is invaginated. Vitelline Fig. 116.—Transverse section of a seventeen-and-a-half-day sheep embryo (Bonnet). by a tuft of capillary blood-vessels from the adjacent primi- tive aortse to constitute a glomerulus (Fig. 117, b b). The pronephric duct passes tailward and opens into the cloaca, a receptacle which receives, in common, the terminal orifice of the primitive bladder and that of the primitive intestine. It is apparent, therefore, that the pronephros or head-kidney is ana- tomically adapted to the function of removing certain sub- stances from the blood by virtue of the action of the cells sur- rounding the glomeruli or tufts of capillary blood-vessels, and that these substances may be conveyed away through the duct into the cloaca and thence evacuated from the body. This organ is functionally active, however, only in certain lower. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Heisler, John Clement; Waterstone, David, former owner; Duke-Elder, Stewart, 18
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