THE EXTERNAL STRUCTURE OF BIRDS. 157 
They are divisible into two sets, namely (A) those which 
spring from the pinion and cover the primary remiges, and (B) 
those which cover the secondary remiges. 
(A) The upper primary coverts spring from the pinion and 
overlie the primaries. By these it can often be determined 
how many primaries a Bird has. There is a series of large 
size, and a second series mostly few in number and scarcely 
visible, being covered almost always by the bastard wing. 
(B) The coverts of the second’ category, or the wpper 
secondary coverts, mostly spring from the fore-arm, and are 
divided into three distinct categories or transverse rows :—- 
(1) The greater upper secondary 'y coverts (tectrices majores) or 
‘“‘oreater coverts.” This category includes the largest and most 
important set of feathers of all the “upper secondary coverts.” 
They form the transverse row which extends f farthest down 
over the secondaries, and afford valuable characters for classifi- 
cation. 
(2) The median upper secondary coverts (tectrices medix), or 
middle coverts, are a transverse row of smaller feathers which 
cover over the bases of the greater coverts. Their apices are 
often otherwise directed than those of the latter. 
(3) The least upper secondary coverts (tectrices minores), or 
lesser coverts, are all the feathers, forming various transverse 
small rows, which cover over the bases of the middle coverts 
and the upper surface of the wing—fore-arm and fold of skin, 
or patagium, attached to it—thence to its anterior margin. 
The humeral coverts are a short series of feathers. arising 
from the skin over the humerus, very well seen in the Duck: 
These coverts are very often absent, and when present they 
may have much of the appearance of innermost secondaries, 
as in the Duck, where they are very long and conspicuous. It 
may also, 1 In some cases, be difficult to distinguish them from 
“‘scapulars,’ but they take origin from the skin over the 
upper-arm bone, more or less external to the humeral pteryla 
where it gives origin to the scapulars. These two categories 
of feathers —scapulars and humeral coverts, can both be seen 
very clearly and distinctly in the Duck. 
The under wing-coverts (tectrices inferiores) are divisible into 
primary and secondary ones like the upper wing-coverts, but 
they are less important for purposes of classification. 
Some of these feathers may, however, be distinguished as 
