ALIMENTARY CANAL. 



439 



proventriculus, which 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 bird^ the gizzard is excellently adapted for the 



Fia. 242. Forms of beaks (a, b c, d, k, after Naumann ; g, i, m, o, Rgne animal ; I from 

 Brehrn). a Phoenicopterus antiquorum ; b Plttalea leucorodi-a ; c Emberiza citrinella ; 

 Turdiis cyanus ; e Falco candicans ; / Mergus merganser ; g Pdicanus perspiciUatus ; h Re- 

 cj'.rrirostra avocetta ; i Rhynchops nigra ; k Columba livia ; I Balaeniceps rex ; m Anastomui 

 coromanddianus ; n Pteroglossus discolor ; o Mycteria senegalensis ; p Falcindlus igneus ; 

 q Cypsdus apus. 



mechanical preparation of the softened food material by the 

 possession of two solid plates, which form the horny internal 

 wall and work against one another. It contains small stones 

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



