ALIMENTARY CANAL. 



439 



proventriculus, whicli is followed by the wide muscular stomach 

 (gizzard). While the proventriculus has, as a rule, an oval form 

 and is smaller than the gizzard, the gizzard is provided with 

 muscular walls, which are weaker (birds of prey) or stronger 

 (granivorous birds), according to the kind of food eaten. In the 

 granivorous birds the gizzard is excellently adapted for the 



Flo. 242. — Forms of beaks (a, h c, d, k, after Naumann ; g, i, m, o, Edgne animal ; I from 

 Brehra). a Pkoenieovterus antiquorum ; b Plttalea leucorodia ; c Emberiza citrinella ; 

 Turdus cyaniis ; e Falco candicans ; / Mergus merganser ; g Pelicanus perspicillatus ; h Re- 

 eurvirostra avocetta ; i Rhynehops nigra ; k Columba livia ; I Balaeniceps rex ; m Anastomus 

 coromandelianiis ; n Pteroglossus discolor ; o Mycteria senegalensis ; ;> Falcinellus igneus ; 

 q Cypselus apus. 



mechanical preparation of the softened food material by the 

 possession of two solid plates, which form the horny internal 

 w^all and work against one another. It contains small stones 

 which the bird swallows to aid in the grinding of the food. The 



