DIGESTIVE SYSTEM OE BIEDS. 



151 



worms, &c. One kind of Humming-bird, feeding on spiders, lias 

 the end of the bill finely toothed. 



Of all bills, the most extraordinary is that of the Cross-bill, in 

 which the extremities of the mandibles curve towards opposite 

 sides and cross each other at a considerable angle — a disposition 

 which at first sight seems directly opposed to the natural inten- 

 tion of a bill. With this singular disposition, the Cross-bill, 

 however, possesses the power of bringing the points of the man- 

 dibles into contact with each other ; and can pick up the smallest 

 seeds, and shell or husk larger kinds like other birds. But the 

 disposition and power of the muscles is such that the bill gains by 

 its very apparent defect the requisite power for breaking up the 

 pine-cones and wrenching out the seeds that constitute its usual 

 food. 



§ 146. Tongues of Birds. — The tongue, as has been already 

 observed, can hardly be considered as an organ of taste in Birds, 

 since, like the mandibles, it is generally sheathed with horn. It 

 is principally adapted to fulfil the offices of a prehensile organ in 

 association with the beak, and it presents almost as many varieties 



Ilyoid and upper larynx^ 

 Swan. 



of form. The length of the tono^ie 

 depends chiefly on that of the 

 glossohyal, fig. 73, 42. In most 

 birds it is lengthened out by a 

 cartilage, ib. «', appended to its 

 extremity. This is remarkable in 

 the Swan and other Lamellirostres. 

 The ceratohyals are obsolete. The basihyal, 4i, contracts as it 

 recedes to support the urohyal, 43, and the hypo- 4G, and cerato- 

 47, branchials are modified to form the posterior cornua or ^ thyro- 

 hyals,' which are of moderate length. The tongue supported by 

 the glossohyal is broad, and furnished Avith a series of retroverted 

 spines, fig. 75, D. In the Humming-bird the horny sheath of 

 the glossohyal is divided at its extremity into a pencil of fine 

 hairs. In the Toucan's tongue, fig. 51, the sheath gives off 

 from the lateral margins stiff' bristle-like processes which project 

 forward : this structure is continued to the apex, and the tongue 

 so provided becomes an instrument for testing the softness and 

 ripeness of fruit, and the fitness of other objects for food, thereby 



