ORGANS ANNEXED TO THE ABDOMINAL DIGESTIVE CANAL. 425 



along with the principal pancreatic duct. The orifices of these two canals 

 are surrounded by a circular mucous fold (ampulla of Fafer), which is 

 usually very prominent, and acts as a valve in preventing the entrance of 

 alimentary substances into the apertures it encircles ; this office it fills so 

 well, that it will not even allow the air with which the duodenum is inflated 

 to pass into the ducts. 



Fig. 216. 



EXCRETORY APPARATUS OF THE HORSE'S LIVER. 



1, Left lobe of the liver ; 2, Middle lobe ; 3, Right lobe ; 4, Lobule of Spigel ; 6, 

 Posterior vena cava at its entrance into the liver ; 7, Vena portae ; 8, Ductus 

 choledochus ; 9, Pancreatic duct ; 10, Common entrance of these two ducts into 

 the small intestine. 



There enter into the structure of the ductus choledochus : 1, A fibrous 

 membrane, which some anatomists believe contains unstriped muscular 

 fibres; 2, Cylindrical epithelium; 3, Numerous racemose glands, opening on its 

 inner surface by very small orifices. 



VESSELS AND NERVES OF THE LIVER. The blood-vessels are the hepatic 

 artery, portal vein, and suprahepatic veins. 



The Jiepatic artery is a branch of the coaliac, and enters the gland by the 

 posterior fissure, in company with the portal vein and ductus choledochus. 

 In the liver it divides into very fine ramifications which join the intra- 

 lobular plexus, anastomose on the surface of the biliary ducts, or expand 

 either on the serous membrane, or in the walls of the portal vein. 



The portal vein is the functional vessel of the liver. It reaches that 

 organ by the posterior fissure, and Glisson's capsule accompanies its rami- 

 fications as far as the hepatic lobules, where they form the plexus of sub- 

 hepatic veins. 



The suprahepatic (or sublobular) veins are so named because they gain 

 the antero-superior face of the viscns to open into the posterior vena cava. 

 They carry away the blood that has been brought by the portal vein and 

 hepatic artery. Their origin is due to the union of the intralobular veins, 

 which make a passage through the hepatic tissue with which their walls are 

 immediately in contact, gradually join each other, and enter the posterior 

 vena cava on its way through the anterior fissure of the liver. The number 

 of trunks (hepatic) entering this vessel is considerable, but the majority are 

 very small ; the principal confluent is placed at the anterior extremity of 

 the fissure. 



The lymphatics form a fine superficial plexus, easy to inject ; with deeper 



