STKUCTUUK Of lUKDS. 5 



liiudtM- tlu'in from expaiuliug or contracliiig' it, and i-('ud<'r.s tla' foot n true fin. Luf^tlv, 

 anidHL;- tlu' liirds wliit'li need a vortical position to clinili, the outer elaw is bi'liind, lie.sidi; 

 the tliund), whence il appears that they have two ting'er.s only in troiil : the panoipict and 

 the jrrci'n woodpecker are instances. 



The impression made upon the mind l)y an I'xamination of a l)ird's external structure, 

 is deepened if its .skeleton be examined, combining, as it dots, great lightncs.s with 

 strength, and that on true mechanical principles. 80 remarkably light is it, that the one 

 of tile white pelican, a bird live feet in length, was fonnd by the Academicians of Paris 

 to weigh only twenty-tlirce omiccs, while the entire bird weighed nearly twenty-five 

 pounds. Had the shoulder bone been one solid piece, its weight ^^oidd have been 

 objectionable, and iniecpial to the strain which it would have to endure, it would soon 

 have snapped asunder; but constructed as a hollow cylinder, it is light, and at the same 







FIG. — 1. Tnt: apti;ryx. 



time strong. Nor is Lightness the only end gained by this hollowness, tor as the bones ot 

 a bird have no marrow, so they are reservoirs for air, and thus peculiarly adapted to the 

 creatures' ordinary mode of life. 



How precisely one bone is adapted to all the rest will be apparent from an interesting 

 fact in the work of an eminent modern writer : — * 



" The incident," he says, " which I am about to mention, exhibits the resiJt of an 

 immense induction of particulars in this noble science, and bears no faint analogy to the 

 magnificent astronomical calcidation, or prediction, whichever one may call it, jiresently 

 to be laid before you. Let it be premised, that Cuvier, the late illustrious French, 

 physiologist and comparative anatomist, had said, that in order to deduce from a single 

 fragment of its structure the entire animal, it was necessary to have a tooth, or an entire 



* " Intolk'ctual and Moral Development of the Present Age." By S. AV'arren. 



