DIGESTIVE SYSTEM OF BIRDS. 



159 



Digestive canal, Common Fowl. 



wliicli consequently a great quantity must be taken to produce 

 the adequate supply of nutriment, and where the cavity of the 

 gizzard is very much dimi- 

 nished by the enormous ' 

 thickness of its muscular 

 coat, the crop is more de- 

 veloped, and takes a more ^^^^^r-^ I'l^^^^i 

 important share in the di- 

 gestive process. Instead 

 of a gradual lateral dilata- 

 tion of the gullet, it as- 

 sumes the form of a glo- 

 bular or oval receptacle 

 aj)pended to that tube, and 

 rests upon the elastic fascia 

 which connects the clavi- 

 cles or two branches of the 

 furculum together. 



In the Common Fowl the crop is of large size and single, 

 fig. 79, h, but in the Pigeon it is double, consisting of two lateral 

 oval cavities, fig. 80, h, c. 

 The dilatation of the 

 oesophagus to form the 

 crop is more gradual in the 

 Ducks than in the Galli- 

 naceous Birds. The crop 

 is wantino: in the Swans 

 and Geese ; but is present 

 in that modified Anserine, 

 the Flamingo. 



The disposition of the 

 muscular fibres of the crop 

 is the same as in the oeso- 

 phagus, but the mucipar- 

 ous follicles of the lining 

 membrane are larger and 

 more numerous. This dif- 

 ference is most conspicuous 

 in the inglu\'ies of the 

 granivorous Birds, Avhere 

 it is not merely a tempo- 

 rary reservoir, but in which 

 the food is mixed Avith the abundant secretion of the glands, and 



Crop of a Pigeon . 



