152 ANATOMY OF THE DOMESTIC FOWL 



oviduct empty into the urodeum. The seminiferous tubules, 

 carrying the semen from the testes in the male empty in teat- 

 like projections on the cloacal mucous membrane into the urodeu- 

 mal portion. The cloacal walls are similar in structure to the large 

 intestines. 



On the dorsal wall of the cloaca between it and the spine, is a 

 small sac, called the bursa ofFabricius, which has a duct communicat- 

 ing with the cloaca. The mucous membrane of this sac is thrown 

 into folds and is studded with glands. The bursa of Fabricus is 

 larger in the young than in the adult bird. It apparently atrophies 

 as the bird becomes older. When the bird is four months old this 

 bursa is best developed, and at this age it may be as large as 2 or 3 

 centimeters in diameter. 



Function. The function of the cloaca is to give passage way to 

 the feces, the urine, and the egg and to act as an organ of copulation. 



Course of the Food. The food first enters the mouth, after being 

 picked up by aid of the beak. From here it passes through the 

 pharynx and first portion of the esophagus to the crop, without 

 mastication, as the bird is not provided with teeth. The food is 

 passed from the crop by aid of its muscular walls as needed; thence 

 through the second portion of the esophagus to the proventriculus, 

 an expansion in the digestive tube just before it terminates in the 

 gizzard. The glands of the proventriculus produce a secretion in 

 which the food is soaked before passing into the gizzard. The 

 gizzard is provided with strong muscular walls which, by aid of grit, 

 thoroughly reduce the food to fineness. From the gizzard the food 

 passes through the first portion of the small intestine, where it is 

 subjected to the action of the bile from the liver, the pancreatic 

 juice from the pancreas, and of the succus entericus from the glands, 

 of the intestinal wall. The food is then passed into the caeca. The 

 indigestible portion of the food passes from the caeca through the 

 large intestine, or rectum, to the cloaca and thence to the external 

 world. 



The digestive functions of the bird are very potent and rapid. 

 This compensates for the waste caused by their extensive, frequent^ 

 and energetic motions, and is in accordance with the rapidity of their 

 circulation and their high state of irritability. 



THE ACCESSORY ORGANS OF DIGESTION 



The accessory organs of digestion are the liver, pancreas, and 

 some anatomists include also the spleen. The first two manufacture 



