126 BIOLOGY OF THE LABORATORY MOUSE 



receive short lateral branches from adjoining cords. These collect into the 

 interlobular bile ducts, which are lined by cuboidal epithelial cells and are 

 in proximity to the branches of the portal vein. As the tributaries of each 

 lobe come together they form the hepatic duct. The common bile duct, 

 formed by the hepatic and cystic ducts, also receives a branch of the 

 pancreatic duct before entering the duodenum. The common bile duct is 

 lined by tall columnar epithelial cells. 



The gall bladder. — The gall bladder is attached to the posterior surface 

 of the median lobe of the liver. It is lined by simple columnar epitheHal 

 cells which have cuticular borders. The thin lamina propria is composed 

 of connective tissue. The mucous membrane forms many folds when the 

 wall is not distended. The irregularly arranged smooth muscle fibers form 

 a very thin layer. A delicate loose connective tissue sheet, part of the 

 peritoneum, covers the free surface of the organ. The cystic duct connects 

 the gall bladder with the common bile duct. 



The pancreas. — The pancreas is a compound acinous gland, composed 

 of many irregularly shaped lobes of varying size, distributed in the mesentery 

 of the duodenum with its distal end in close proximity with the spleen. 

 The lobes are covered by a thin connective tissue membrane which also 

 divides them into lobules. The small secretory acini, which resemble those 

 of the parotid gland, are composed of polyhedral shaped cells with dark 

 staining round nuclei near the bases. Below and around the nucleus the 

 cytoplasm stains deeply with basic stains, while above it the cytoplasm is 

 light and contains granulations (zymogen). Mitotic figures are rare 

 although they occur occasionally. Cytological variations exist due to the 

 difference in the functional phase of the gland, and perhaps also due to 

 the fact that the gland undergoes post mortem changes very quickly. 



The secretion is collected in minute intercalated ducts lined by flat 

 epitheHal cells. As these ducts enter the acini they appear to be continuous 

 with the centro-acinous cells. These cells are flattened, have relatively 

 large, dark staining nuclei and a small amount of cytoplasm. The intra- 

 lobar ducts are lined by cuboidal epithelial cells. One duct of the gland 

 enters the common bile duct, while another enters the duodenum close 

 to the entrance of the bile duct. At the entrance of the pancreatic duct into 

 the duodenum small groups of pancreatic acini are usually present in the 

 submucosa of the duodenum. In obese animals adipose cells are found 

 in the interstitial tissue of the gland. 



Irregularly distributed among the acini or the interstitial tissue are 

 the pancreatic islands (of Langerhans), which function as glands of internal 



