﻿54 



ON THE CLASSIFICATION OF BIRDS. 



tongue, of less importance than those leading forms we 

 have now described ; but as our space will not allow of 

 extending our remarks upon this organ, we shall at once 

 proceed to notice others. 



(54.) The Mouth, or rictus, is of greater or less ex- 

 pansion, according to the description of food upon which 

 the bird subsists, or the method of taking it, although 

 in the generality of species the mouth is not of great 

 extent; its angles or sides, when the jaws or mandibles 

 are closed, do not reach so far back as to pass the base 

 of the eye, supposing a perpendicular line to be drawn 

 from one end to the other. But in birds having a very 

 wide mouth, the basal angle of the jaws passes far 

 behind this imaginary line, and the mouth is said to 

 open beneath the eye. The smallest mouths are seen 



it represents the class of Acrita, in the great circle of 

 the animal world, where the mouth is for the most part 

 altogether wanting. It is in conformity with this law 

 that the humming birds, being suctorial, have the small- 

 est mouths in the insessorial order ; for as they swallow 

 those insects only which are very minute, a greater 

 extension is not necessary. Birds, on the contrary, 

 which capture their prey upon the wing, and gulp it 

 down immediately, have mouths of enormous width. 

 The whole tribe of the Fissirostres, at the head of 

 which are the swallows, may be instanced as possessing 

 this structure, carried, perhaps, to a greater extent in 

 the night-jars (Caprimulgidce, fig. 22. 6) than in any 



U {fig- 22. a), and in the 



in the grallatorial order, 

 where we have the plovers 



WgSff types by which it is re- 



presented in other circles. 

 This is strictly conform 

 able to that law of va- 

 riation in structure before 

 explained, by which this 

 primary type is so distin- 

 guished ; because, in fact, 



