186 Mr. Yarrell on the Analomt/ of Birds of Prey. 



true Falcons, possess, with (heir exclusive rapidity of flight, any 

 power of vision beyond their generic companions, would be diffi- 

 cult to ascertain \ but it may, while on this subject, be worthy of 

 remark, that the iridcs of the Gyrfalcon^ Peregrine, Hohhy^Mer' 

 lin and Kestrily are hazel brown, or still darker, while those of all 

 the hawks, buzzards, harriers and kites, are of various shades of 

 yellow. I refer only to adult birds, and do not remember a 

 single exception. A representation of the bony ring and crystal- 

 line lens of the Golden Eagle is here given, as shewing the gene- 

 ral form of these parts in the genus Falco, and as a contrast to the 

 shape of the same parts ia the genus SMx, to be hereafter des- 

 cribed. The number of bony plates forming this circle in the 

 Golden Eagle is fifteen^ in thei White-tailed Eugle there are but 

 fourteen. 



The trachea in the different species of the genus Falco, exhibits 

 none of those peculiarities of form observable in the species of some 

 other genera. It is composed of two membranes enclosing between 

 them numerous bony rings, forming a tube more or less perfect 

 from end to end. These bony rings are strong and compressed. 

 The point of divarication, the cross-bone and bronchiae, consti- 

 tuting together the inferior larynx, are of the most common form, 

 having but one pair of muscles attached; and the voice, though 

 powerful, possesses, as might be expected, but little variation. 

 The oesophagus oifers nothing peculiar beyond that of other birds, 

 not possessing the power of minutely dividing their food. It is 

 plicated lengthways, allowing great extension, and its separation 

 from the stomach is marked by a zone of gastric glands. 



The stomach in birds exhibits every gradation which the various 

 qualities of their food might seem to require, from the thin mem- 

 branous pouch of the bird of prey, to the true muscular gizzard of 

 the Gallinaceous tribe and others. Of the nature of the gastric 

 fluid, and its effects on various substances in different animals, the 

 experiments of Spallanzani have thrown considerable light, but 

 the subject is far from being exhausted. 



An opportunity which occurred to me of observing the castings 

 or pellets of some eagles, which had been occasionally fed with 

 dead pigeons, shewed, that the vegetable food, peas, wheat, and 



