THE DIGESTIVE TRACT. lgl 



comprise an outer fibrous adventitia and an inner mucous 

 membrane. The latter, in addition to the columnar epithelium, 

 consists of the tunica propria, containing 

 many elastic fibres and some delicate FIG. 226. 



bundles of involuntary muscle, irregu- 

 larly disposed as circular and longitudi- 

 nal bundles. Small mucous glands also 

 occur within the mucosa of the larger 

 canals and of the hepatic duct. The inter- 

 lobular bile-ducts may be distinguished 

 from blood-vessels of the same size by 

 their lining of columnar epithelium. 



The blood-vessels of the liver, as 

 already described, are of primary impor- Transverse section of large bile-duct 

 tance in determining the arrangement J^S^SSS 

 of the hepatic tissue. The blood brought areoiar tissue, 

 by the interlobular branches of the portal 



vein passes into the lobule at the periphery by the numerous twigs ; 

 these, on entering the lobule, form a closely anastomosing intra- 

 lobular capillary net-work, which converges to a central intra- 

 lobular vein. The central vessel is vertically placed with regard to 

 the general plane of the capillary net-work, and empties into the ad- 

 jacent sublobular veins, which are branches of the hepatic vein, 

 lying within planes generally at right angles to those of the portal 

 vessels. 



The hepatic artery has directly nothing to do with the elabora- 

 tion of the especial products of the organ, its particular province 

 being to supply the blood for the nutrition of Glisson's capsule 

 and of the interlobular structures, including the blood-vessels and 

 the bile-ducts. Minute arterial twigs are distributed to the walls of 

 these tubes, where they end in delicate capillary net-works, which, 

 in turn, at the periphery of the lobule, pour their contents into the 

 intralobular net-work of the portal vein. 



The lymphatics of the liver constitute a superficial and a deep 

 system. The superficial lymphatics accompany the branches of 

 the arteries supplying the capsule, and form a close-meshed sub- 

 serous net-work within the capsule. 



The interlobular blood-vessels are accompanied by numerous lym- 

 phatics, whose ramifications and anastomoses constitute the deeper 

 plexus. The presence of lymphatics within the parenchyma of the 

 liver is still a matter of dispute. According to Disse, the lym- 

 phatic channels exist throughout the lobule as perivascular canals, 

 surrounding the capillaries and separating them from direct contact 

 with the secreting cells. 



