164 MANUAL, OF PHYSIOLOGY. 



are: (1) The gall bladder is its receptacle for storing the secre- 

 tion until it is required. (2) It has a double supply of blood. 

 Besides that coming from the spleen, pancreas and intestinal 

 canal, collected by the tributaries of the great portal vein, and 

 distributed by its branches to the liver, it receives by the hepatic 

 artery a small supply of fresh arterial blood. (3) A beautiful 

 network is formed by the minute ducts (bile capillaries) which 

 freely anastomose between the cells. (4) Although in the em- 

 bryo, and in many animals throughout their adult life, the liver 

 is a compound saccular gland, yet the relation of the duct radi- 

 cles to the saccules is so modified in the higher animal and man, 

 that the analogy is no longer apparent, and the structural ar- 

 rangement is best understood by following its vascular ground- 

 work. 



Structure of the Liver. On the surface of the liver are 

 seen small rounded markings about the size of a pin's head which 

 give the organ a peculiar mottled appearance. This is much 

 more striking in some animals (giraffe, bear, pig) than others, 

 but easily recognizable in the livers of all mammalia. These 

 little areas mark out the lobules of the liver. They are sur- 

 rounded by a dark red boundary, and their centre is marked by 

 a dark spot, between which there is a paler yellowish zone. The 

 dark parts correspond to the bloodvessels, and have a constant 

 relation to the lobules. 



The entire liver is made up of these little lobules, and each 

 one of them has the same construction and blood supply, and 

 therefore forms in itself a little liver perfect in all its structural 

 arrangements, so that the description of one such unit will 

 suffice to give an idea of the structure of the liver. For other 

 details, anatomical works must be referred to. 



The branches of the large portal vein and those of the small 

 hepatic artery pursue the same course through the gland, and are 

 inclosed in a sheath of connective tissue, which also forms the 

 bed of the hepatic duct and its numerous tributaries. If these 

 branching vessels be followed to their final ramifications, they are 

 found to pass around and between the neighboring lobules. The 



