216' THE DOG-FISH 



The valve serves to retard the passage of food 

 down the intestine, and to increase the extent of 

 its absorptive surface. 



B. The Glands. 



1. The liver has been described above. 



a. The gall-bladder is a large irregular sac imbedded 



in the anterior part of the left lobe of the liver, 

 close to the median plane. 



b. The bile-duct leaves the gaU-bladder between the 



two lobes of the liver, and almost in the Eiiedian 

 plane. It receives ducts from the lobes of the 

 liver, and runs back along the ventral margin of 

 the mesentery to the iatestine, along which it 

 runs for a short distance to open iato the com- 

 mencement of the colon. The bile-duct has a 

 total length of about three inches. 



Find the duct along the edge of the fold of mesentery 

 between the li/oer and the intestine : make an incision in its 

 walls, and either insert a bristle into it or inject it with a 

 coloured fluid su^ch as Prussian blue : follow it forwards to 

 the liver and gall-bladder, and bachwa/rds to its operdng into 

 the intestine, 



2. The pancreas is a whitish, laterally compressed body 



about an inch and a half long, lying in the angle 

 between the distal Hmb of the stomach land the 

 intestine. Its anterior end is expanded and gives 

 off a small ventral lobe, which is closely apphed to 

 the iatestine. 



a. The pancreatic duct runs forwards through the pan- 

 creas close to its ventral border. It leaves the 

 gland at the posterior angle of its ventral lobe, 

 and at once enters the ventral wall of the intes- 

 tine about an inch beyond the pylorus : it runs in 

 the wall of the intestine for about half an inch, 

 and opens just to the outer side of the line of 

 attachment of the spiral valve. 



