INTRODUCTION. 17 



that procure their food on the land. Birds, therefore, can- 

 not strictly be arranged according to their manner of walk- 

 ing or flying, any more than according to their food ; but all 

 these circumstances, and others, taken in connexion with 

 their organization, lead to the formation of orders and fami- 

 lies, which are in themselves more or less natural, that is, 

 contain a series of species obviously connected with each 

 other more than with other species. 



In this Synopsis of the Birds of England, Scotland, and 

 Ireland, the arrangement proposed is into Orders, Families, 

 Genera, and Species, the characters of the more comprehen- 

 sive divisions alluded to above, are not given ; but as it was 

 found expedient to divide it into two volumes, it was thought 

 best to give the general title of Land-Birds to the Volato- 

 rial and Gradatorial series, and that of Water-Birds to the 

 Grallatorial and Natatorial. 



In the Introduction to the first volume, some necessary 

 explanations were given relative to the general structure and 

 form of birds, their different parts, their dermal system, in- 

 cluding the plumage, mandibles, and claws, and their diges- 

 tive organs. On the present occasion it is not requisite to 

 continue the subject farther than to say a few words respect- 

 ing the structure of the intestinal canal, and the trachea, 

 which present very remarkable modifications in the different 

 groups, and of which some afford even specific distinctions. 



The width of the mouth corresponds with the size of the 

 object to be swallowed ; but one cannot always judge of its 

 capability of admitting a large mass by its mere appearance, 

 for a mouth may seem narrow, which is yet capable, by the 

 elasticity of the parts, of being greatly expanded. The 

 tongue generally aids in the prehension and deglutition of 

 the food, and varies according to its nature, but also has 

 evident relation to the form of the cavity in which it is 

 lodged. When the tongue is extremely small, as in Cor- 

 morants and Gannets, it is useless with reference to prehen- 

 sion, and, in such cases, the bird must toss up the object 



