EXTEnNAL ANATOMY. TOES. 
119 
it first appears only as a posterior scale, double the size 
of the others. As the bird increases in age, so does 
this scale increase in size and elevation, until it finally 
becomes a solid acute spur. W e pass over several other 
variations of the tarsal scales, as seen in different groups, 
and now proceed to other parts of the legs. 
(109.) The Toes of birds, by their leading varia- 
tions, furnish the primary characters by which the whole 
class is divided into orders, and the subordinate modi- 
fications of their structure indicate, for the most part, 
natural groups. In this respect they consequently de- 
serve even more attention than the tarsi. We have 
already described the peculiarities of retractile, perch- 
ing, walking, wading, and swimming feet, and shall 
therefore at once proceed to enumerate their several 
variations. The great majority of birds have four toes 
to each foot, three of which are usually placed before, 
and one, which is called the hnllux, or hinder toe, is 
placed in a backward direction. The exceptions to this 
number of toes, and to their disposition, are compara- 
tively few ; the most remarkable instances, as regards 
the nmnber, are found in the ostrich family (Struthi- 
onidm). The toes of the* ostrich are only two, one 
large, the other small : this extraordinary structure, for 
a bird, is in perfect harmony with its station in the 
great scheme of creation, for it is by means of this 
animal, half quadruped, half bird, that nature passes 
from the feathered class to that of the mammalia ; and 
yet, although the ostrich would appear absolutely de- 
prived of all those powers which enable birds to escape 
from their enemies, either by perfect wings or highly 
developed toes, she has nevertheless made the ostrich, 
with its two toes, one of the swiftest running birds in 
creation. The cassowary, the emu, and the Ame- 
rican rhea, have three toes upon each foot, but the 
latter only has the vestige of a fourth, which merely 
shows itself in the form of a tubercle ; but in the 
Apternyx, or New Zealand emu, the most aberrant of 
the ostrich family, we find the hinder toe, although 
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