606 ORGANS OF SECRETION. 



from the mixed blood conveyed by the united capillaries of 

 the vena portae and hepatic artery, the diameter of the ulti- 

 mate divisions of the tubuli, as in other glands, much ex- 

 ceeding that of the capillary blood vessels which afford them 

 the materials of the secretion. But although the more trivial 

 circumstances of the size and mode of grouping of the tubuli, 

 and the outward form and bulk of the entire mass, vary in 

 the different tribes of mammalia, and the mode of distribu- 

 tion of the blood vessels through the organ, we still find this 

 largest and most complicated gland to consist, in the highest 

 as in the lowest animals, merely of a membranous duct, or 

 prolongation developed from the parietes of the alimentary 

 canal, destined to augment the secerning surface, for the 

 more extensive distribution of capillaries, and to form a more 

 convenient reservoir of this stimulating and solvent secre- 

 tion. From the chemical composition of the bile, the liver 

 appears to perform a function somewhat similar to that of 

 the lungs, and its development in animals is generally in the 

 inverse ratio to that of their respiratory organs. 



The secretion of the liver, which in the lowest animals is 

 poured directly into the stomach, to reach the food early, 

 and to act upon it during the whole of its short passage 

 through the body, now always enters the alimentary canal at 

 some distance beyond the stomach, the food being here acted 

 upon by numerous other secretions, and having a long 

 course to pass through after leaving the stomach. As all 

 parts of the liver, like the parts of the lungs or other secret- 

 ing organs, have the same function to perform, they are 

 shaped or fissured into lobes, according to the forms of the 

 surrounding parts or other convenience in the different 

 tribes, being least lobed in the inactive abdomen of the low- 

 est aquatic mammalia, the cetacea, more divided in the 

 herbivorous quadrupeds, and most fissured in the active 

 trunks of many carnivora and rodentia, where its primitive 

 peripheral lobules sometimes remain distinct through life. 

 But even the external forms and peripheral divisions of 

 glands, manifest the same uniformity of plan, as other the 

 most trivial parts of the economy, as the position of the 

 intestinal turns in the abdomen, the cerebral convolutions 

 in the cranium, or the direction of the hairs on the several 

 parts of the skin. 



The gall-bladder is most generally deficient in the her- 



