14 GUIDES FOR VERTEBRATE DISSECTION 



tine behind. Insert a blowpipe in the anus and inflate the 

 urinary bladder in the posterior part of the peritoneal cavity. 



Sketch these viscera without disturbing them. 



Study the parts more carefully. See that the whole cavity is 

 lined with a smooth membrane, the peritoneum, and that this 

 covers the enclosed viscera as well. Insert a probe in the oesoph- 

 agus, then turn the liver to the right and note the posterior end 

 of this tube. Just inside the ccelom the alimentary canal enlarges 

 to form the stomach, which is somewhat U-shaped. Its two 

 ends have received special names. That joining the oesophagus 

 is the cardiac, the other the pyloric end. Note the constriction 

 (pylorus) at the pyloric end, formed by a sphincter muscle. 



Follow the course of the intestine backwards from the stomach, 

 taking pains not to tear the membranes binding the various 

 parts of the alimentary tract together and to the body wall. 

 The first portion of the intestine, paralleling the pyloric part 

 of the stomach is the duodenum. The rest of the tube, of about 

 the same size throughout, is the small intestine. Near the 

 posterior end there comes a sudden enlargement, the rectum, 

 which proceeds backwards until the urinary bladder is reached, 

 where this enlarged portion is known as the cloaca, a region which 

 extends to the anus. 



See the membranes which bind the alimentary canal together 

 and to the body wall. Those connecting the different parts 

 of the tract are called omenta, those connecting the canal to 

 the body wall are mesenteries. The mesentery supporting the 

 stomach is the mesogaster, that of the small intestine the mesentery 

 proper, that of the rectum the mesorectum. The hepato-duodenal 

 omentum connects liver and duodenum, the gastro-duodenal 

 omentum lies between stomach and duodenum, and the gastro- 

 hepatic omentum between stomach and liver. 



Examine the liver more carefully. How many lobes are 

 there? See on the postero-dorsal surface of one of its lobes the 

 spherical gall-bladder (greenish in life). Trace the bile-ducts 

 from it into the liver and into the intestine. 



Look in the gastro-duodenal omentum for the elongate 

 pancreas. Does it extend into the mesentery or into any other 

 omentum? Look in the mesentery between the rectum and the 

 bend of the stomach for the round, dark-colored spleen. 



Make a more detailed drawing of the alimentary tract. 



