14 A BOOK OF BIRDS 



terminating in little hooks (figs. 5b and 6) ; further, the portion bearing 

 these booklets is twisted, so as to take a vertical instead of a slant- 

 ing position. The series of barbules which run along the other 

 side of the ramus, or '* barb," are known as the posterior barbules, 

 and differ entirely in shape from those of the anterior series just 

 described. Like the anterior series, however, they may be described 

 as ribbon-shaped ; but they are curled so that the lower edge touches 

 the lower segment of the curve next in front of it, thus forming a 

 series of troughs, as in fig. 6, where they are seen in section. The 

 upper edge of each of these curved plates, you will notice, is turned 

 over scroll-fashion, and further, as in fig. 5a, it will be seen that the 

 plate is bent upon itself near its middle and is notched along its 

 lower edge. 



Fig. 5b.— A Distal Radius. 



V / H. Hamuli or Hooklets. 



Fig. sa.— Proximal Radii. ^m. V / c.' ciiia or Barbiceis. 



F. Folded edge. ^^j. M 



Now, when in position, the bent ends of the posterior series are 

 stowed away under a sort of roof, formed by the slanting, ribbon-like, 

 overlapping bases of the anterior series ; while the hooklets of the 

 anterior series are thrust down into the troughs formed by the posterior 

 series, and, further, so that they catch hold of the scrolled edges of 

 this series (fig. 6). Mark that these scrolls, or troughs, are kept 

 apart by a very wonderful yet simple contrivance, to wit, the series of 

 " teeth," or notches, near the end of the upper edge of each bar- 

 bule shown in fig. 5a ; but for these, the edges would rub together 

 and cut off the hooklets. In some birds of powerful flight a 

 strengthening band runs along, from the lower edge of the barb 

 to the lower edge of that next behind it (fig. 6, P). This serves to 

 keep the barbs in position during the strain of flight. 



Thus, then, this marvellous interlocking is the reason why it is 



