GIZZARDS OF BIRDS. 



169 



provided in most of the insects belonging to the 

 order of Orthoptera ; but I shall not enter at 

 present in their description, as it will be more 

 convenient to include them in the general ac- 

 count of the alimentary canal of insects, which 

 will be the subject of future consideration. 



The internal machinery for grinding is exem- 

 plified on the largest scale in granivorous birds ; 

 where it forms part of the stomach itself, and is 



termed a Gizzard. It is 

 shown in Fig. 298, repre- 

 senting the interior of the 

 stomach of a Stvan. Both 

 the structure and the mode 

 of operation of this organ 

 bear a striking analogy 

 to a mill for grinding 

 corn, for it consists of two 

 powerful muscles (g), of a 

 hemispherical shape, with 

 their flat sides applied to each other, and their 

 edges united by a strong tendon, which leaves a 

 vacant space of an oval or quadrangular form 

 between their two surfaces. These surfaces are 

 covered by a thick and dense horny substance, 

 which, when the gizzard is in action, performs 

 an office similar to that of mill-stones. In most 

 birds, there is likewise a sac, or receptacle, 

 termed the Crmv, (represented laid open at c) in 

 which the food is collected for the purpose of its 



