. Text-book of embryology. Embryology. 188 EMBKYOLOGY OF THE LOWEE VEETEBEATES Fig. 108.—Illustrating early development of the liver in Birds. A, 47-hour chick; B, 52-hour chick ; C, 50-hour chick (after Brouha, 1898); D, fourth-day chick; E, 7 mm. embryo of the Roseate Tern—SterTia paradisiaca— (after Hammar, 1897). bd1, rudiment of anterior (" left") bile- duct; 6d2, posterior ("right") bile-duct; ent, cavity of fore-gut; gb, rudiment of gall-bladder; li. 1 and 2, anterior and posterior liver - rudiments ; pan, l dorsal rudiment of pancreas. portion of the rudiment.
. Text-book of embryology. Embryology. 188 EMBKYOLOGY OF THE LOWEE VEETEBEATES Fig. 108.—Illustrating early development of the liver in Birds. A, 47-hour chick; B, 52-hour chick ; C, 50-hour chick (after Brouha, 1898); D, fourth-day chick; E, 7 mm. embryo of the Roseate Tern—SterTia paradisiaca— (after Hammar, 1897). bd1, rudiment of anterior (" left") bile- duct; 6d2, posterior ("right") bile-duct; ent, cavity of fore-gut; gb, rudiment of gall-bladder; li. 1 and 2, anterior and posterior liver - rudiments ; pan, l dorsal rudiment of pancreas. portion of the rudiment. The gall bladder originates as a bulging of the floor of the bile-duct towards its anterior end. The formation of the pos- terior and longer section of the bile-duct, which will be extrahepatic in the adult, lags in its development behind the anterior portions of the rudiment. Such differences in the time of appearance of different parts of the hepatic apparatus—liver, gall-bladder, bile-duct—are to be looked on as mere secondary modifica- tions of development, — the primitive condition being that of a simple pocket of the gut- wall such as persists in Am- phioxus. Saueopsida.—The hepatic apparatus here again makes its appearance as a longi- tudinally situated pocket of the morphologically ventral wall of the gut. In birds this is situated at first on the anterior wall of the yolk-stalk (Fig. 108, A). The diverti- culum grows actively into an anterior (dorsal) and a pos- terior (ventral) pocket (Fig. 108, C, li. 1 and li. 2) while the intervening portion be- comes flattened out and incor- porated in the gut-wall. There thus come to be two distinct liver-rudiments an anterior and a posterior. Of these each sprouts out at its end into irregular projections which eventually fuse and form a spongy mass, surround- ing the cavity of the ductus venosus, and having in its meshes blood-spaces which. Please note that these images are extracted from scanned page images that
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