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DESCRIPTIVE ORNITHOLOGY. 
CLASS—AVES, BIRDS. 
Birds, as a class, can be divided into toothed and toothless birds, 
although the former are now extinct and are known only by their frag- 
mentary remains preserved as fossils. All modern birds are toothless. 
Some species, as the mergansers, are furnished with serrations in the horny 
bill that have a superficial resemblance to teeth (Figure 7, p. 19), but 
examination shows that these are not true teeth. 
SUBCLASS—CARINATA. KEEL-BREASTED BIRDS. 
Present day, toothless birds are divided into two subclasses, the 
Ratite or raft-breasted birds and the Carinate or keel-breasted birds. The 
Ratite include the Ostriches and Emues which are without a keel to the 
breast bone for the attachment of wing muscles and are flightless. There 
are none in North America and they are, therefore, not dealt with here. 
The term keel-breasted is derived from the high, thin, keel-like projection 
from the middle of the breast bone, to which the powerful breast or wing 
muscles are attached. 
Keel-breasted birds (subclass Carinate) are divided into numerous 
orders which are considered in the sequence adopted by the American 
Ornithologists’ Union. 
Order—Pygopodes. Diving Birds. 
General Description. The Divers, as their name implies, are birds fitted for subaquatic 
pursuits. The hip joint is set far back on the body and the leg mechanism is better fitted 
for swimming than for walking. The tarsus, the visible part of the leg, is much flattened, 
(Figure 2, p. 18), and the toes are either partly (Figure 138, p. 20) or completely (Figures 2 
and 6, p. 19) webbed. The wings are small in comparison with the size of the body. The 
bill is straight and generally tapered, moderately long, but occasionally flattened and 
deepened, as in the cases of the Auks and Puffins; in the latter species this specialization 
reaches its highest development in the order. 
Distinctions. Toes, three or four entirely or partly webbed, tarsus flattened, tail 
inconspicuous or small. 
Field Marks. Small wings and tail and straight, narrow, unduck-like bills. The 
a bear a superficial resemblance to ducks but where the ducks would fly the Divers 
ive. 
Nesting. In the immediate vicinity of water on reedy shores or rocky ledges, or in 
crevices and holes in the ground. 
In consequence of the peculiar leg construction, an unusually upright 
carriage of the body is necessitated when on land, and they walk with 
difficulty. Indeed some species are almost helpless on the ground and are 
unable to rise into the air except from the water, off steeply rising ground, 
or against a strong head wind. They swim and dive with ease and, though 
their wings are small in comparison to the size of the body, when once on 
the wing they fly with rapid beats, swiftly and strongly, in straight lines 
or long curves without evolution or manceuvring. 
