ORDER II . 
INSESSORES. 1 
In accordance with the views of many systematic writers, it may perhaps be as well to retain 
an order Insessores, and to place in it the Strisores, Clamatores, and Oscines as sub-orders. The 
characters of the order will then consist chiefly in the possession of three toes in front and one 
behind, (or at least never with two toes directed backwards,) as in Scansores. The claws are 
not retractile, nor the bill with a cere, as in the Baptores ; nor is the hind toe situated appreci- 
ably above the plane of the others, as in Basores, Grallatores, and Natatores. 
The hind toe of the Insessores corresponds to the thumb or inner toe of the mammals, and is 
usually quite short. The joints of the anterior toes generally follow the law of number charac- 
teristic of birds, namely, two to the hinder, three to the inner, four to the middle, and five to 
the outer toes ; but a deviation is seen in some Strisores where there are sometimes but three 
joints each to the anterior toes, and sometimes only four in the outer. The tarsi are generally 
covered anteriorly with plates, and furnished behind with granulations or small scales, or else 
with two long plates covering the sides, the latter feature especially characteristic of the 
Oscines, or singing birds ; in the latter alone is the tarsus sometimes covered anteriorly with 
a single plate. Sometimes the tarsus is entirely or partly naked, or destitute of plates altogether. 
The carpal joint or the hand part of the wing is in most Insessores furnished with ten quills* 
(primaries,) although the first quill is sometimes very short or even entirely wanting, as in 
many Oscines. The fore arm has from six (in the humming birds) to thirteen quills, the 
average being eight or nine. 
There are certain peculiarities in the arrangement of the wing coverts of the different sub- 
orders of Insessores, constituting important distinctive features. Some of these will be hereafter 
referred to. 
The tail of the Insessores exhibits considerable differences. The number of feathers is usually 
twelve ; sometimes ten only, as in the Strisores. 
The different groups of the order Insessores are subject to considerable variations in respect to 
the structure of the lower larynx attached to the trachea or wind pipe just anterior to its division 
into the two bronchial tubes. Cuvier long since showed that the true singing birds had the 
larynx provided with a peculiar apparatus 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 
sub-divisions, as will be shown hereafter, depend very much on these peculiarities of the larynx. 
The tongue of the Insessores varies to a considerable degree. In the humming birds it is 
thread-like and bifurcated. In most other insessorial or perching birds it is long or short, flat, 
1 The following remarkson the general charac rs of the Insessores are derived chiefly from Burmeister'a Thiere Brasiliens, 
Vogel, page 305. 
