THE DOGFISH 9 



Note that the hinder portion of the intestine is not joined 

 with the dorsal body wall by a mesentery, except at its extreme 

 hinder end. Note the elongated, cylindrical rectal gland, which 

 lies in this mesentery. Find the duct which joins it with the 

 rectum. 



Observe again the large stomach. The anterior end passes for- 

 ward beneath the liver and is joined with the pharynx by a very 

 short and equally thick oesophagus. Pass a probe from the pharynx 

 into the stomach. The anterior end of the stomach is called the 

 cardiac end. The posterior, V-shaped portion of the stomach is 

 continuous with the intestine, the posterior end of it being called 

 the pyloric end. 



Trace the bile duct from the liver to its point of union with the 

 intestine, which is a short distance posterior to the pyloric end 

 of the stomach. 



The intestine is made up of three portions,— the duodenum, 

 colon, and rectum. The duodenum is very short and forms the 

 anterior end of the intestine ; it receives the bile duct. The colon 

 forms the principal portion of the intestine and is characterized 

 by the presence in it of an extensive spiral fold of the mucous 

 membrane, called the spiral valve. This fold extends from the 

 inner wall of the intestine and almost fills it ; its attachment to 

 the intestinal wall is plainly seen on the outside. The rectum is 

 short and extends from the colon to the cloaca. It is joined by a 

 short duct from the rectal gland. 



Exercise 9. Draw a semidiagrammatic sketch of the digestive system. 

 Represent accurately the shape of the liver and the pancreas, and 

 the bile and pancreatic ducts. Carefully label all these parts. 



Study the spiral valve. Make a longitudinal slit in the ventral 

 wall of the colon and duodenum. The spiral valve will be seen 

 to be a wide fold which extends into the cavity of the colon from its 

 inner surface, forming a series of spirals nearly filling it. They 

 have the appearance of a nest of elongated cones, one inside the 

 other and opening backward. Beginning at its hinder end, cut the 

 spiral valve from the intestinal wall with scissors. It will be seen 

 to be a single fold. 



