: 
SYSTEMATIC SYNOPSIS 
OF 
NORTH AMERICAN BIRDS’? 
Subclass I. AVES AEREZ, or INSESSORES. 
AERIAL BIRDS, or PERCHERS. 
Tue first and highest one of three primary divisions of the classt Aves, embrac- 
ing all existing birds down to the Galline. 
The knee and part of the thigh are free from the body, and the leg is almost 
always feathered to or beyond the tibio-tarsal joint. With rare exceptions, the 
toes are all on the same level, and touch the support throughout; being thus fitted 
for grasping or perching. In other respects the members of this great group are too 
various to be defined by external characters, unless it be negatively, in the absence 
of the special features of the other two groups. They are Altrices. They are now 
usually divided into jive Orders, of which the first is the 
Order PASSERES. Perchers Proper. 
The feet are perfectly adapted for grasping by the length and low insertion of 
the hind toe, great power of opposing which to the front toes, and great mobility 
of which, are secured by separation of its principal muscle from that that bends 
the other toes collectively. The hind toe is always present, and never turned for- 
* North of the present Mexican Boundary; inclusive of Lower California; exclusive of Greenland. 
tAs commonly received, without recognizing, however, the fossil Archwopteryx (see Introd. § p. 12) a meso- 
zoic bird, which probably alone represents a primary group Saurure; admitting which, some high authorities 
then divide all existing birds into two other primary groups, atite (Ostriches), in which the sternum has no 
keel, and Carinate, embracing all other birds. On this basis, our Aves aéree would represent a group of less 
value than a subclass; and I desire to be understood as using this term provisionally, in a conventional sense, 
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