ALIMENTARY CANAL AND ASSOCIATED ORGANS 

 OF THE FROG 1 



1. Secure the specimen previously dissected. Cut off and discard the 

 portion of the lower jaw which lies anterior to the glottis. Next cut 

 through the mucous membrane lining the dorsal part of the mouth cavity, 

 just posterior to the openings of the Eustachian tubes. Be careful not to 

 disturb the underlying bony structures of the upper jaw. You have now 

 freed the anterior end of the esophagus from the body. 



2. With your forceps, gently lift up the lower jaw with the attached 

 esophagus and then, beginning anteriorly, carefully cut all the mesenteries 

 which attach the alimentary canal to the body. Make a transverse cut 

 through the anterior end of the rectum. Now remove the entire alimen- 

 tary canal with the attached liver and pancreas from the body, taking 

 care not to disturb the underlying urogenital organs. Place the organs 

 which you have just removed in a dissecting pan and pin them out so as 

 to show to the best advantage. It may be necessary to cut some of the 

 mesenteries. 



3. Examine the alimentary canal throughout its entire length. Identify 

 and note the structure of the (a) esophagus ; (6) stomach ; (c) pyloric 



VALVE ; (d) SMALL INTESTINE ; (e) PANCREAS with the PANCREATIC DUCT, 



which joins the bile duct from the gall bladder of the liver before the 

 latter opens into the small intestine ; and (/) the large intestine, which 

 merges into the cloaca. Draw to show the various structures as observed. 



4. Examine, with the low and high power, a prepared transverse 

 section of Frog intestine. Note that it is composed of a number of 

 layers as follows : (a) the thin, outer covering (serosa) ; (b) the mus- 

 cular layers consisting of an outer longitudinal layer and a thicker, 

 inner circular layer; (c) the connective tissue layer (submucosa), 

 and (d) the epithelial layer (mucosa) which is thrown into folds, and forms 

 the inner lining of the intestine. The mucosa consists of two types of 

 elongated epithelial cells, namely, the absorptive cells, and the secre- 

 tory cells, or unicellular glands. The latter type may be distin- 

 guished by the presence of a secreting area in each. Draw the section 

 in outline and fill in a portion to show the detailed structure of the various 

 layers. 



i B. pp. 184-189. 

 331 



