770 



THE LIVER. 



It is still doubtful whether the hepatic cylinders are as a rule hollow or 

 solid. In Elasmobranchii they are at first provided with a large lumen, 

 which though it becomes gradually smaller never entirely vanishes. The 

 same seems to hold good for Amphibia and some Mammalia. In Aves 

 the lumen of the cylinders is even from the first much more difficult 

 to see, and the cylinders are stated by Remak to be solid, and he has 

 been followed in this matter by Kolliker. In the Rabbit also Kolliker finds 

 the cylinders to be solid. 



The embryonic hepatic network gives rise to the parenchyma 

 of the adult liver, with which in 

 its general arrangement it closely 

 agrees. The blood-channels arc 

 at first very large, and have a 

 very irregular arrangement ; and 

 it is not till comparatively late 

 that the hepatic lobules with their 

 characteristic vascular structures 

 become established. 



The biliary ducts are formed 

 either from some of the primi- 

 tive hepatic cylinders, or, as 

 would seem to be the case in 

 Elasmobranchii and Birds (fig. 

 422), from the larger diverti- 

 cula of the two primitive out- 

 growths. 



The gall-bladder is so incon- 

 stant, and the arrangement of 

 the ducts opening into the intes- 

 tine so variable, that no general statements can be made about 

 them. In Elasmobranchii the primitive median diverticulum 

 (fig. 421) gives rise to the ductus choledochus. Its anterior end 

 dilates to form a gall-bladder. 



In the Rabbit a ductus choledochus is formed by a diver- 

 ticulum from the intestine at the point of insertion of the two 

 primitive lobes. The gall-bladder arises as a diverticulum of 

 the right primitive lobe. 



The liver is relatively very large during embryonic life and 

 has, no doubt, important functions in connection with the circu- 

 lation. 



FIG. 422. DIAGRAM OF THE DIGES- 

 TIVE TRACT OF A CHICK UPON THE 

 FOURTH DAY. (After Gotte.) 



The black line indicates the hypo- 

 blast. The shaded part around it is 

 the splanchnic mesoblast. 



Ig. lung ; <,(. stomach ; /. pancreas ; 

 /. liver. 



