246 DIGESTION. [CHAP. xxv. 



passing through the former channel must permeate a totally distinct 

 system of vessels, namely, the lacteal system, to be conveyed to the 

 superior vena cava and to the right auricle, where having mingled 

 with the blood coming from the liver, both are transmitted by 

 the right ventricle to the lungs. 



And it would seem that the object of the two modes of ab- 

 sorption at the intestine, and of the two paths or transmission 

 from the intestine to the centre of the circulation, is to keep 

 separate, up to a certain point, two kinds of material resulting 

 from the digestion of the food. And probably the reason why one 

 kind of product is reserved to pass through the intricate capillary 

 plexuses of the vascular system of the liver, to the exclusion of the 

 other, is because it contains material out of which the liver may 

 elaborate bile ; whilst the other material is transmitted through 

 a less complicated series of channels more directly to the lungs. 



Of the Offices of the Pancreas and Liver in Digestion. The pre- 

 sence of two such great glands as the pancreas and the liver, existing 

 in a large portion of the animal kingdom at the upper part of the 

 intestinal canal, and pouring their secreted fluid into it, obviously 

 denotes a connexion between the fluids secreted by these glands, and 

 the changes which the food undergoes in this part of the intestine. 



As the function of the pancreas has been determined with greater 

 accuracy than that of the liver, it will be more convenient to con- 

 sider it first. 



Function of the Pancreas in Digestion. The presence of the 

 pancreas is constant, at least, in the vertebrate classes. 



It is present in all the mammalia it is, perhaps, better deve- 

 loped in carnivora than herbivora ; in all, it is in intimate relation 

 with the upper part of the small intestine, into which it pours its 

 secretion by one or two ducts. In some, as in man, the pancreatic 

 duct and the common choledoch duct open into the duodenum at 

 the same place ; in others they open at some distance from each 

 other (as much as sixteen or seventeen inches in the rabbit) but in 

 all they open into the same portion of the intestinal canal; and 

 the pancreatic duct, always below the biliary duct, when they do 

 not open together. Some doubt exists as regards its presence in 

 fishes. In rays and sharks a solid gland exists, corresponding to 

 the pancreas ; and in osseous fishes a similar gland has recently 

 been discovered by Stannius which appears to be its analogue.* 



The secretion of the pancreas has some semblance to saliva. It 

 * Miiller's Archiv., 1849. 



