“ SMITHSONIAN MISCELLANEOUS COLLECTIONS [voL. 48 
5. The Tertiary Fibers 
Between the secondary quills lie two systems of fine fibers, which 
in their close connection form the greater part of the feather plate 
that acts on the air in flight. The tertiary fibers spring from the 
upper part of both sides of the secondary quills, and form two little 
fiber-vanes (fig. 22). In a work by Schroeder (1880, pp. 3-14) 
there is a critical discussion of all papers on this subject published 
up to 1880. Nitzsch (1840, pp. 5-15) was the first to give a fairly 
correct description of these structures, with a number of good draw- 
ings. In 1887 Wray made an attempt to construct an enlarged model 
of a feather and from it prepared some very schematic drawings 
(TE87, pl. scr): 
Among works of later date are Ahlborn’s (1896, pp. 17-21) and 
Strong’s papers (1902, pp. 156-161), to which and to a small num- 
ber of others I shall have occasion to refer. What has been said 
with regard to the nomenclature of the secondary quills holds good 
for the tertiary fibers also. Uniformly termed “ barbules”’ in Eng- 
lish and French, they figure in German works promiscuously as 
“ Strahlen,” “ Nebenstrahlen,’ “ Faserchen,” “ Fiedern II. Ord- 
nung,” “ Fiederchen,’ etc. We must distinguish two essentially 
different kinds of tertiary fibers, one being on the whole straight 
and bearing on the ventral side several hooks, the hook-fibers (fig. 
21, Hkf); the others being curved and without hooks, the curved 
fibers (fig. 21, Bgf). This division of the fibers into two kinds 
seems to be justified also by the fact that they start from different 
sides of the secondary quills. 
If we cut sections through the feather vane, according to the 
method before described, in the direction of the hook-fibers, or in 
that of the curved fibers, in the first case, between the transverse 
sections of every two adjacent secondary quills we get a longitudinal 
section of a hook fiber and a series of transverse sections of curved 
fibers, and in the other case, a longitudinal section of a curved fiber 
and a series of transverse sections of hook-fibers (figs. 24,25). The 
series of transverse sections of different parallel fibers thus obtained 
are identical with a series of transverse sections of the same fiber. 
Accordingly, we can reconstruct from these sections any particular 
fiber we like. 
A. Hook-Fibers 
The structure of the hook-fibers is as follows. The proximal por- 
tion is band-like, transversely curved so as to become groove-like, 
the concavity of the groove being turned towards the secondary quill, 
from which the fibers arise (fig. 26). This band-like basal portion 
