. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. 3°6 THE LIVER In the early stages the endodermal lining of the digestive tract assumes a considerable thickness, the lumen of the oesophagus and upper part of the small intestine being reduced to a very small caliber. In later stages a rapid increase in the size of the lumen occurs, apparently associated with the formation of cavities or vacuoles in the endodermal epithelium. These increase in size, the neighboring cells arrange themselves in an epithelial layer around their walls and they ev
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. 3°6 THE LIVER In the early stages the endodermal lining of the digestive tract assumes a considerable thickness, the lumen of the oesophagus and upper part of the small intestine being reduced to a very small caliber. In later stages a rapid increase in the size of the lumen occurs, apparently associated with the formation of cavities or vacuoles in the endodermal epithelium. These increase in size, the neighboring cells arrange themselves in an epithelial layer around their walls and they eventually break through into the general lumen. They are sometimes sufficiently large to give the appearance of diverticula of the gut, but later they flatten out, their cavities becoming portions of the general lumen. In the case of the duodenum the thickening of the endodermal lining proceeds to such an, extent that in embryos of from mm. to mm. the lumen is completely obliterated immediately below the opening of the hepatic and pancreatic ducts. This condition is interesting in connection with the occasional occurrence in new-born children of an atresia of the duodenum. Under normal conditions, however, the lumen is restored by the process of vacuolization described Fig. 187.—Reconstruction of a Portion of the Intestine of an Embryo of 28 mm. showing the longitudinal folds from which the villi are formed. {Berry.) The Development of the Liver.—The liver makes its appear- ance in embryos of about 3 mm. as a longitudinal groove upon the ventral surface of the archenteron just below the stomach and between it and the umbilicus. The endodermal cells lining the anterior portion of the groove early undergo a rapid proliferation, and form a solid mass which projects ventrally into the substance. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustr
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