PLATYPUS AND ECHIDNA. 



be wholly in the portal interval, which lies between the 

 inner extremities of the right and left lateral lobes. A 

 fine peritoneal fold is noted passing from the ventral 

 surface of the gall bladder and cystic duct to the lesser 

 omentum. At the portal interval it is joined by two main 

 hepatic ducts on each side, viz. right and left hepatic. 

 Into the left hepatic duct three main branches pass from 

 left mesial, left lateral, and spigelian lobes ; into the right 

 hepatic three main branches also pass, viz. from the right 

 mesial, right lateral, and caudate lobes. At the portal 

 interval the portal vein is posterior and the artery slightly 

 to the left between the two. The combined or common 

 bile duct then passes in the right extremity of the lesser 

 omentum for about 5 cm., lying at first between the lobus 

 caudatus and spigelian lobe and enters the duodenum 

 about 2.5 cm. from the pyloric knob. The pancreatic 

 duct opens into the common bile duct obliquely about 

 2-2.5 cm. from its termination in the duodenum and fol- 

 lowing somewhat the curve of the duodenum is traced on 

 the left in the pancreatic tissue to the spleen receiving 

 tributaries in its course. At the junction the common 

 bile duct is seen to be almost double in its circumference 

 that of the pancreatic duct. Thereafter, the circumfer- 

 ence of the combined hepatico-pancreatic duct is almost 

 double that of the common bile duct. At its termination 

 the duct loops slightly to the left. The opening into the 

 duodenum is minute and may be indistinguishable from 

 the inner surface of the duodenum till the duct is opened 

 and a hair seeker passed through. Furthermore, near 

 the termination of the duct a valvular projection is to be 

 seen, by which apparently the flow of bile is regulated. 

 This valve lies .5 cm. from the termination. Between the 

 valve and the duodenal wall the duct forms a dilatation, 

 but on passing through the bowel wall it narrows again. 



14 



