188 EMBKYOLOGY OF THE LOWEE VEETEBEATES oh. 



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). bd 1 , rudiment of anterior (" left ") bile- 

 duct ; 6d 2 , 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 



