DIGESTIVE SYSTEM 221 



between the distal limb of the stomach and the 

 intestine. Its anterior end is expanded and gives 

 off a small ventral lobe, which is closely applied to 

 the intestine. 



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 

 attachn^ent of the spiral valve. 



Find the duct along the ventral border of the pancreas r 

 trace it to the intestine : slit open the intestine, and trace the 

 duct hachwards in its wall as a ivhite ridge ending- in a very 

 small papilla. It is easier to follow after injection with a- 

 coloured fluid. 



3. The, rectal gland is a thick-walled tube, about three' 

 quarters of an inch long, lying in the abdominal cavity 

 dorsal to the rectum. From its hinder end a duct 

 runs forwards along the edge of the mesentery to 

 open into the dorsal wall of the rectum. 



Gut the gland across about the middle of its length. Note 

 the thickness of its walls and the small size of its caMty, 

 Pass a bristle down the gland and duct into the rectum ; and 

 slit open the rectum to see the opening of the duct. 



V. DISSECTION OF THE EESPIBATOEY SYSTEM. 



The dog-fish breathes by gills, which are vascular folds 

 of the mucous membrane of the pharynx, supported by the 

 branchial arches. Respiration is effected by streams of water, 

 which, entering at the mouth, pass between the branchial 

 arches, over the gills, and out through the gill-clefts. 



1. The gills. 



Expose the gills on the left side by prolonging the external 

 apertures upwards and downwards with scissors. 



