6 INTRODUCTION. 



narrated by one or more authors, add to their store of know- 

 ledge, or find relaxation from more important occupations. In 

 composing the present work I have kept in view the interest of 

 the scientific as well as the general student ; and while I have 

 entered into the details of structure and form, I have paid 

 equal attention to the manners and habits of the different 

 species. 



As to their arrangement, I have thought it prudent, in the 

 present unsettled state of opinion on the subject, and under 

 the conviction that all existing systems are defective, to adopt 

 the opinions of no systematist, but to group the species accord- 

 ing to their obvious relations. Although the number of spe- 

 cies that occur in Britain is not sufficiently great to aiFord a 

 connected view of the entire series of genera and families, yet 

 it is sufficiently so to admit of observations respecting their 

 connection and mutual affinity. The Rapacious Birds gene- 

 rally occupy the first rank in systems, and I am not aware of 

 any good reason for depriving them of it ; but as I have lately 

 submitted to the public a description of them, and as it may be 

 more advantageous to begin with a tribe of birds having a 

 more remarkable construction of the digestive organs, which I 

 conceive to have been too much neglected by ornithologists, I 

 shall first treat of the Gallinaceous birds and Pigeons. 



In all arrangements of birds hitherto published, whether 

 professing to be derived from the consideration of the aggre- 

 gate of the organization, or from particular organs, the modifi- 

 cations in the form of the bill have afforded the principal 

 characters. After much consideration, however, and after 

 examining the digestive organs in a great number of birds 

 belonging to nearly all the families, I have resolved to adopt 

 the intestinal canal as a central point of reference. Instead, 

 then, of describing merely the bill, I attend to the mandibles, 

 the mouth, the tongue, the throat, the oesophagus, the crop, 

 the proventriculus, the stomach, the intestine, and the coecal 

 appendages ; the modifications of which seem to me to throw 

 more light upon the affinities of the larger groups than those 

 of any other organ. 



In some systems the modifications in the form of the feet 



