Development of the Third Day 211 



" The liver continues to grow rapidly, and by the 

 tenth day is the largest organ in the abdominal cavity. 

 The trabecular network of hypoblast cells becomes 

 the liver parenchyma ; the tubular diverticula from the 

 duodenum branch out freely in the substance of the 

 liver, and become the two bile ducts of the adult bird ; 

 while the gall bladder arises on the fifth day as a sac- 

 cular outgrowth from the right or larger of the two 

 primary diverticula. 



"The early formation of the liver in the chick, and 

 its large size during the greater part of the develop- 

 mental history, indicate that it must be of considerable 

 functional importance during embryonic life. Its rela.- 

 tion to the blood system, and especially the fact that it 

 intercepts the blood returning from the yolk-sac to the 

 heart, suggest that its chief purpose is connected with 

 the elaboration of food material which is obtained from 

 the yolk-sac, and at the expense of which the nutrition 

 of the embryo is effected." 1 



The pancreas arises a little later than the 

 liver, as a tubular diverticulum from the in- 

 testine just back of the liver (Fig. 67, /). A 

 second diverticulum is formed at about the 

 eighth day, and, still later, a third appears. 

 These diverticula persist as the three pancre- 

 atic ducts of the adult, but the lobes with 

 which they are connected fuse together. 



The thyroid body. At the close of the 



1 Marshall. 



