THE BIRDS 



I8 7 



ming bird which is used to probe the necks of flowers for 

 small insects or* honey represents another type which 

 is strongly contrasted with the short bill of night hawks 

 and swallows, adapted for catching insects on the wing. 

 A curious modification is seen in the crossbills in which the 

 tips of the jaws are curved and crossed. This arrangement 

 is peculiarly adapted for extracting from open pine cones 

 the seeds upon which the crossbills feed. The largest 



FIG. 146. The toucan. 



bills among birds occur in the toucans, or horn-bills, which 

 live in South America. 



As birds have no teeth they do not chew their food; 

 while the objects may be broken up more or less by the 

 bill they are usually swallowed whole. The function of 

 grinding up food is performed by the gizzard which is a 

 very strong muscular division of the alimentary canal. 

 Usually birds that live more or less upon hard seeds swal- 

 low a quantity of gravel which aids in the grinding process, 

 In many birds the esophagus expands below the base of 

 the neck into a thin-walled crop in which a quantity of food 

 is carried and then gradually passed back to the gizzard. 

 After being ground up in the gizzard and partly digested 



