432 THE DIGESTIVE APPABATV8 IN MAMMALIA. 



on tie other hand, has demonstrated that there is always an augmentation 

 in the spleen's volume when an animal has ingested large quantities of 

 water, the consecutive absorption of which determines a certain tension in 

 the portal venous system. 

 ' The second opinion, emitted by KoUiker, is founded on the existence 

 in the splenic pulp of blood-globules in a state of decomposition, and 

 in the analyses made by J. Beclard of the blood in the splenic vein, 

 which have proved that there is a notable diminution in the proportion of 

 globules. 



It is to be remarked that, in the researches undertaken to discover 

 the functions of the spleen, account has not been taken of the connections 

 existing between this organ and the great omentum in the majority of 

 mammals, and which testify that the spleen is only, properly speaking, 

 a vascular appendage placed on the track of this omentum. But the uses 

 of this vast peritoneal fold are themselves little understood. Might they 

 not be included with those which are presumed to belong to its appended 

 organ ' 



diffehential chabactees in the annexed oegans in the abdominal poetion of 

 the digestive canal in other than soliped animals. 



The important differences these organs offer in the domesticated mammals belong 

 more particularly to the liver. 



1. Liver. — In the domesticated mammals other than Solipeds, the liver exhibits vari- 

 ations in form, volume, and position, which have no influence on its organisation : so that 

 the study of these possesses but a mediocre attraction. This is not so, however, with re- 

 gard to the excretory apparatus, the arrangement of which is complicated, and becomes 

 very interesting. The biliary duct, in fact, on leaving the fissure of the portal vein, and 

 before reaching the intestine, gives rise to a particular conduit which is detached at an 

 acute angle, and which, after a course of variable length, according to the size of the 

 animal, becomes dilated into a vast sac, the so-called gall-bladder. 



Ill all treatises on anatomy, the special conduit is designated the cystic duct, that 

 portion which precedes its origin being named the hepatic duct ; while the appellation of 

 ductus communis choledochus is reserved for the section which goes to the intestiue. But 

 these distinctions are vicious, and we limit ourselves to the recognition of: (a) A ductus 

 choledochus exactly lOie that of Solipeds, and like it extending from the posterior 

 fissure, where it originates by the union of several branches, to the duodeniun ; and (6) a 

 cystic duct, which branches suddenly iuto the choledic duct, and terminates in the gall- 

 hladder. 



a. The gall-bladder is a reservoir with membranous walls, in which the bile accumu- 

 lates during the intervals of digestion. This sac, lodged wholly, or in part, in a fossa on 

 the posterior face of the liver, is oval or pyriform, and presents a fundus and neck. Its 

 parietes comprise three tunics : an external, of peritoneum : a middle, formed of dartoid 

 tissue ; and an internal, or mucous, continuous with that of the various biliary ducts. 



6. The cystic duct extends in a straight line from the neck of the gall-bladder to the 

 choledic duct. It adheres intimately to the tissue of the liver, and does not exhibit, in- 

 ternally, the spiral valves which have been described in Man. In opening it longitudi- 

 nally, there are discovered, at least in Ruminants and the Camivora, very small orifices 

 which pierce the wall adherent to the tissue of the liver : these are the openings of 

 several minute but particular biliary canals, named the hepatico-cystic ducts. 



c. The ductus communis clwledochus comports itself exactly as in Solipeds. It is 

 much wider than the cystic duct, and opens sometimes alone, sometimes with the pan- 

 creatic canal, into the duodenum in a manner which, up to a certain point, reminds one 

 of the mode of termination of the ureters. Instead of passing perpendicularly across the 

 intestinal parietes, it first pierces the muscular layer, follows for a short distance between 

 it and the mucous membrane, and then opens on the internal face of the latter by an 

 orifice which is encircled by a valvular fold, as in the Horse. 



Such is the excretory apparatus belonging to the liver in animals provided with 

 a gall-bladder. In these animals the biliary secretion is certainly continuous, as 

 in the Horse ; but in the intervals of digestion the bile, instead of flowing directly on 

 to the intestinal surface, passes iuto the gall-bladder by the cystic duct, and there 



