508 



THE DIGESTIVE APPARATUS IN MAMMALIA. 



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 course 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 ? 



Differential Characters in the Organs Annexeti to the Abdominal Portion of 

 THE Digestive Canal in the other Animals. 



Fig. 302. 



The important diiferences these organs offer in the domesticated Mammals are more 

 particularly observed in the liver. 



1. Liver. — In the domesticated Mammals other than Solipeds, the liver exhibits variations 

 in form, volume, and position, which have no influence on its organization : so that the study 

 of these possesses only a moderate amount of interest. This is not so, however, with regard 

 to the excretory apparatus, the arrangement of which is complicated, and becomes very inte- 

 resting. 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 (Figs. 302, 303). 



In all treatises on anatomy, the special conduit is 

 designated the cyxtic (or bile) 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 intestine. But these 

 distinctions are vicious, and we limit ourselves to the 

 recognition of: (a) A ductus choledochus exactly like 

 that of Solipeds, and like it extending from the pos- 

 terior fissure, where it originates by the union of several 

 branches, to the duodenum ; and (b) a cystic duct, which 

 branches suddenly into the choledic duct, and terminates 

 in the gall-bladder. 



a. The gall-bladder (Fig. 302, 1) is a reservoir with 

 membranous walls, in which the bile accumulates 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 peri- 

 toneum; a middle, formed of fibrous tissue; and an 

 internal, or mucous, continuous with that of the various 

 biliary ducts. 



b. Tiie cystic duct (Fig. 302, 2) 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, internally, tiie spiral valves which have been described in Man. In 

 opening it longitudinally, tiiere are discovered, at least in Ruminants and the Carnivora, very 

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

 of several minute, but special, biliary canals, named the hepatico-ctjstic ducts. 



c. The ductus communis choledochus (Fig. 302, 3) comports itself exactly iis in Solipeds. It is 

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

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

 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 



LIVER OF THE OX. 



, Interior extremity of the liver; 

 B, superior extremity ; C, Spigelian 

 (caudate) lobe. 1, Gall-bladder; 

 2, cystic duct; 3, ductus chole- 

 dochus ; 4, root of that duct ; 5, 

 posterior vena cava ; 7, intestine ; 

 8, insertion of the pancreatic duct. 



