DIGESTIVE ORGANS. 233 
The bile is passed to the intestine by the bile duct (choledochal or 
hepatic duct), but the other products are carried away by the blood 
(internal secretion). 
The anlage of the liver is a ventral diverticulum irom: the archenteron 
(p. 206), which grows forward from its point of origin, branches again 
and again, the ultimate branches forming the glandular part of the 
organ, the proximal parts of the outgrowth giving rise to the bile duct 
(ocasionally multiple) which empties into the intestine. As a result of 
this method of formation the liver is to be regarded as a compound 
tubular gland, the lumens of the tubules forming the gall capillaries 
which eventually empty into the duct. This tubular condition is 
readily recognized in the ichthyopsida, but itis masked in the amniotes 
and especially in the mammals, in part by the anastomosis of the 
tubules, in part by the interrelation of the bile and blood-vessels. 
With development the liver grows cephalad from its point of origin, 
but this forward growth is limited by the presence of the blood-vessels 
which develop the sinus venosus and the hepatic veins and also contrib- 
ute to the septum transversum (hepatic 
veins—see circulation), and so its later 
increase must cause it to grow in the op- 
posite direction. As it increases in size 
there is an immigration of mesenchyme 
between the lobules and with these the 
Fic. 240. Fic. 241. 
Fic. 240.—Diagram of two types of bile ducts. 6, gall bladder; ch, choledochar duct; 
h, hepatic ducts; 7, intestine. 
Fic. 241 —Liver and pancreas of American ostrich (Rhea) after Gegenbaur. d, duo- 
denum; dh, bile ducts; /, liver; oe, oesophagus; p, pancreas; pd, pancreatic duct; s, stomach. 
blood-vessels enter. At the same time the liver grows away from the 
alimentary canal, carrying the peritoneum before it so that it receives 
an outer serous coat. 
Usually the bile duct (when there are several ducts only one is con- 
cerned) forms a lateral diverticulum, the gall bladder, which serves as 
a reservoir for the bile. This is usually placed on the dorsal side of the 
