THE LIVER. 455 



into the mesoblast. The apex of the funnel leads into the 

 duodenum. From this arrangement it results that at this period 

 the original outgrowth from the duodenum serves as a recep- 

 tacle into which each ductule of the embryonic gland opens 

 separately. I have not followed in detail the further growth of 

 the gland. It is, however, easy to note that while the ductules 

 grow longer and become branched, vascular processes grow in 

 between them, and the whole forms a compact glandular body 

 in the mesentery on the dorsal side of the alimentary tract, and 

 nearly on a level with the front end of the spiral valve. The 

 funnel-shaped receptacle loses its original form, and elongating, 

 assumes the character of a duct. 



From the above account it follows that the glandular part 

 of the pancreas, and not merely its duct, is derived from the 

 original hypoblastic outgrowth from the gut. This point is 

 extremely clear in my preparations, and does not, in spite of 

 Schenk's observations to the contrary 1 , appear to me seriously 

 open to doubt. 



The liver. 



The liver arises during stage I as a ventral outgrowth from 

 the duodenum immediately in front of the opening of the 

 umbilical canal (duct of the yolk-sack) into the intestine. 

 Almost as soon as it is formed this outgrowth developes two 

 lateral diverticula opening into a median canal. 



The two diverticula are the rudimentary lobes of the liver, 

 and the median duct is the rudiment of the common bile-duct 

 (ductus choledochus) and gall-bladder (PI. n, fig. 9). 



By stage K the hepatic diverticula have begun to bud out a 

 number of small hollow knobs. These rapidly increase in length 

 and number, and form the so-called hepatic cylinders. They 

 anastomose and unite together, so that by stage L there is con- 

 structed a regular network. As the cylinders increase in length 

 their lumen becomes very small, but appears never to vanish 



(PL 19, fig. 5). 



The mode of formation of the liver parenchyma by hollow 

 and not solid outgrowths agrees with the suggestion made in 



1 Lehrbuch d. vergleichenden Embryologie. 



