244 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



two bile-ducts, the left short and wide, running into the duodenum 

 near its commencement, while the right, long and narrow, opens 

 into its distal limb near the beginning of its distal third. There 

 is no gall-bladder. 



A gall-bladder is present in the Fowl. The bile and pancreatic ducts are 

 also arranged differently. 



The pancreas is a compact, elongated body, lying in the loop 

 of the duodenum, and sending three pancreatic ducts into its 

 distal limb. 



As in the frog, the alimentary canal is suspended from the 

 dorsal wall of the body-cavity by mesenteric folds. The mem- 

 branous lining of the abdominal region (which, however, is quite 

 continuous with that of the thorax) is the peritoneum. This 

 closely lines the dorsal side of the cavity before leaving its walls 

 to form mesenteric folds. 



The wall of the alimentary canal is made up of the usual four 

 coats mucous, submucous, muscular, and serous. The mucous 

 membrane possesses an epithelial lining varying in the different 

 parts of the canal. That found in the mouth-cavity and parts of 

 the oesophagus is stratified squamous epithelium, and that lining the 

 crop glandular. The lower parts of the gullet, the proventriculus, 

 and the intestines are lined by simple columnar epithelium, con- 

 tinued into the simple tubular peptic glands of the second, and 

 there becoming glandular. Glands of Lieberkiihn are present in 

 the small intestine. The epithelium of the gizzard secretes a 

 thick horny cuticle. 



The muscular coat varies very much in thickness, and typically 

 consists of two layers, an internal circular and an external longi- 

 tudinal, the relative position of these being reversed, however, in 

 the gullet. This coat is immensely thickened in the gizzard, 

 and has there a complicated arrangement. 



The serous coat is an epithelial and connective-tissue layer 

 present from the proventriculus backwards, and formed by the 

 investing mesentery. 



The liver and pancreas present no important deviations from 

 the structure of the same organs in the frog (pp. 193, 194). 



The food, chiefly consisting of grain, accumulates in the crop, 

 from which it passes on through the proventriculus to the gizzard, 

 which grinds it up, the process being aided by the foreign bodies 



