324 



COMPARATIVE ANATOMY 



(Fig. 272). While branches of the vagus nerve reach the liver, most of its 

 nerves belong to the sympathetic system. 



In most microscopic preparations of the liver the branching tubules 

 appear as solid cords of epithelial cells. In microscopic preparations 

 made by the Golgi method, however, the bile capillaries which carry the 

 secretions of the liver cells are stained black and contrast strongly with 

 the lightly colored cells. In such preparations, the bile capillaries are 

 seen to be minute passages between the gland cells leading to the inter- 



FiG. 271. — Liver of a pig. The lobules have artificially shrunken from the inter- 

 lobular tissue, a; b, bile duct; c, hepatic artery; d, interlobular vein (a branch of the 

 portal); e, trabeculae ; /, central vein. (From Bremer's "Text Book of Histology," after 

 Radasch.) 



lobular ducts and the hepatic ducts, which carry the secretions to the gall 

 bladder where they are temporarily stored. (Fig. 270) 



The gall bladder is a pear-shaped muscular sac between three and four 

 inches in length, holding about 30 cc. Its inner surface is lined by a 

 mucous epitheUum which is thrown into folds. Crescentic folds in the 

 neck of the bladder and in the common bile duct form a sort of spiral 

 valve. When food enters the duodenum from the stomach, the muscles of 

 the gall bladder squeeze the bile into the intestine. This action is some- 

 times impeded by gall stones formed by constituents of the bile such as 

 cholesterol. Pressure from the intestine caused by constipation may 

 have the same effect, and result in "bilious" disorders. 



