GLANDS. 417 



In all follicular glands, the secreting cells are situated on 

 the internal surface of the basement membrane : in the liver, 

 however, they are placed upon its external surface, the true 

 basement membrane terminating with the termination of the 

 biliary vessels. 



Mr. Bowman regards the innumerable series of secreting 

 cells as representing the continuation of the biliary ducts, 

 and a rudimentary condition of which he considers them to 

 be ; in the same manner as linear series of granular cells re- 

 present, according to some observers, the rudimentary form of 

 other vessels and tissues ; as, for example, the muscular fibre 

 and the primitive nerve tubule. 



Vascular Apparatus. 



The vascular apparatus of the liver has been well under- 

 stood since the period of the publication of Mr. Kiernan's 

 Researches. This apparatus consists of hepatic veins, portal 

 vein, and hepatic artery. 



Hepatic Veins. The venas cavse hepatica? commence in 

 the centre of each lobule of the liver by a plexus of capil- 

 laries, which penetrates it in all directions ; these uniting, 

 form larger vessels, and which, again, join together, to con- 

 stitute the central lobular vein : this escaping from the lobule 

 altogether, becomes what has been termed the sublobular 

 vein, and it next unites with other sublobular veins to f(5rm 

 the main branches of the hepatic veins. (Plate LY.^. 1, 2.) 



Portal Veins. The portal vein is mainly formed by the 

 union of the inferior and superior mesenteric veins; and 

 these, again, have their origin principally in the confluence of 

 the capillary vessels of the villi of the small intestines. 



The portal vein enters the substance of the liver at the 

 transverse fissure. After numerous ramifications, many of its 

 branches are spread over the outer surface of the lobules : 

 these Jbranches are called the interlobular veins : from these 

 branches others still smaller proceed ; these, penetrating the 

 substance of the lobules, break up into capillaries, which unite 

 with the capillaries of the lobular hepatic veins, already spoken 



L L 2 



