INTRODUCTION. 21 



It is remarkable, that many fish-eating birds have an ex- 

 tremely slender and elongated intestine, while others have 

 it moderate in both respects, and in others it is both long 

 and wide. . Why these differences should exist, is not very 

 apparent ; but I have observed, that in all those piscivorous 

 birds which plunge headlong or dart upon their prey, it is 

 very slender. Even among the Falconinae, the species 

 which feed on fishes, as the Osprey and Sea-Eagle, have the 

 intestine thus modified. 



The vocal and respiratory organs, being alluded to in the 

 ordinal characters, may be now briefly noticed. In all birds, 

 the trachea, or windpipe, is composed of a series of complete 

 cartilaginous or bony rings, constituting a flexible tube, ca- 

 pable of being shortened or elongated by the action of two 

 lateral muscles, and the peculiar manner in which the rings 

 are made alternately to overlap each other. The upper 

 aperture of this tube forms a longitudinal slit, which is 

 opened or closed by muscles acting upon the cartilages or 

 bones which form its frame. It is in this upper or anterior 

 part, the larynx, that the voice is produced in the mamma- 

 lia ; but in birds, although the larynx and mouth may mo- 

 dify the voice, its peculiar organ is the lower part of the 

 trachea, where it divides into the two bronchi which go to 

 the lungs. The last ring is divided by a bony partition, 

 and furnished with membranes, the action of the expired air 

 on which causes sound. The modulations of sound are pro 

 duced here by the action of small muscles upon the rings 

 and membranes. Birds which emit merely a scream, or un- 

 modulated sounds, have no peculiar muscle at this part ; such 

 are Vultures, Swifts, Pheasants, Partridges, Pelicans. Those 

 which emit sounds slightly varied have a single pair of mus- 

 cles ; as Hawks, Woodpeckers, Pigeons, Rails, Gulls, and 

 Divers. Some have two pairs, as Parrots ; the Kingfishers 

 have three pairs ; and all the Cantatrices, Deglubitrices, and 

 Vagatrices, have four pairs. The form of the inferior la- 

 rynx varies much, being small or large, compressed, flat- 



