4O MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



Liver. The liver, as was said above, develops as a divertic- 

 ulum from the ventral side of the primitive alimentary canal. 

 This outgrowth branches again and again, the result being a 

 greatly branched tubular gland, the proximal portion of the 

 tubes being specialized as the ducts leading to the intestine. 

 In the amphibia and reptiles this tubular condition is retained 

 throughout life, the minute lumen of the glandular portions 

 being known as the gall capillaries. In birds and mammals 

 the tubular condition soon disappears, the gall capillaries run- 

 ning, without much regularity, between the cells. By the in- 



c 



FIG. 44. Hepatic ducts of A, frog; B, emeu; and C, cat. A, ampulla of 

 Vater; B, gall-bladder; C, cystic duct; DC, ductus choledochus; H, hepatic ducts; 

 HE, hepatoenteric duct; W, duct of Wirsung (pancreatic). 



growth of connective tissue the liver glands are divided into 

 lobules, the so-called ' liver islands.' In this connective tissue 

 run the larger gall ducts (which connect with the gall capil- 

 laries), and also branches of the hepatic artery and of the por- 

 tal vein (see circulation). From their position these vessels 

 are often spoken of as interlobular. In the centre of each 

 island (intralobular in position) is a branch of the hepatic vein, 

 while capillaries extend through the lobules from the inter- 

 lobular to the intralobular blood-vessels. As a rule, there is 

 but a single duct emptying from the liver into the intestine, 

 and this, as a rule, has connected with it by a lateral branch 

 (cystic duct) a thin-walled gall-bladder. When these condi- 

 tions occur, the duct leading from the liver as far as the mouth 



