ALIMENTARY CANAL. 



439 



proventriculus, which is followed by the wide muscular stomach 

 (gizzard). While the proventriculas 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, b c, d, k, after Naumann ; g. i, m, o, RSgne animal ; I from 

 Brelira). a Phoenicovterus antiquorum ; b Platalea leucorodia ; c Emberiza citrineUa ; 

 Turdus cyanits ; e t'alco candicans ; / Mergus merganser ; g PcHcanus perspiciUatus ; h He- 

 curiirostra avocetta ; i Rlv/nchops nigra ; kColumha livia : I Balaeniceps rex ; m Anastnntus 

 coromandeliunus ; n Pteroglossus discolor ; o Mycteria sene-galensis ; p Falcinellus igneus ; 

 q Cypseliis 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 



