ORDER III. — INSESSORES. 100 



The tail of the Insessores exhibits considerable differences. 

 The number of feathers is usually twelve ; sometimes ten onlv, as 

 in the Strisores. 



The different groups of the order Tyisessores are subject to con- 

 siderable variations in respect to the structure of the lower larynx 

 attached to the trachea or windpipe just anterior to its division 

 into the two bronchial tubes. Cuvier long since showed, that the 

 true singing-birds had the larjmx provided with a peculiar appa 

 ratus for the purpose of effecting a modulation of the voice, 

 composed of five pairs of muscles, of which other birds were 

 destitute in greater part, or entirely. The characteristic of the 

 groups Strisores, Clamatores, and Oscines, and of their subdivisions, 

 as will be shown hereafter, depend very much on these peculiarities 

 of the larynx. 



The tongue of the Insessores varies to a considerable decree. 

 In the Humming-birds, it is thread-like and bifurcated. In most 

 other insessorial or perching birds, it is long or short, flat, and 

 triangular, the posterior extremity bilobed, the anterior usually 

 with the tip horny, serrated, or with fibres, more rarely smooth. 

 These furnish important characteristics for the division into families, 

 and even genera ; the variations being quite considerable. 



iSee Introduction, and vol. IX., Pacific R.R. Reports, 128. 



