16 DRAGONFLIES OF NORTH AMERICA 
parallel to the radial sector, and the other (Mj) parallel to the main 
radial stem (R:). 
The cubitus (Cu) is a two-branched vein. Like the median vein, 
it is strongly zig-zagged. Its base is free and straight to the arculus 
or beyond. Then it bends sharply to rearward, forming the inner 
(proximal) side of the triangle (¢). At the hind angle of the triangle 
it forks, and its branches arch outward running more or less parallel 
to reach the hind margin. 
The anal vein (A) is here treated as a single vein though its branches 
are perhaps the equivalent of the separate anal veins of other orders 
of insects. It is convenient to designate them as Aj, A», Az, etc., from 
front to rear. The course of these branches varies greatly in the 
different groups, and sometimes in fore and hind wings. 
There are three principal transverse joinings of veins together in 
the dragonfly wing: 
aS ITI 
» PO a 
s. R 
= Mw 

Fig. 4. Diagram illustrating principal veins and their connections. 
(1) The outermost is the stigma (st). Two veins (C and R) are here 
united by a heavy quadrangular deposit of chitin, that adds strength 
and weight at the point of greatest impact of the wing against the air. 
(2) The middle conjunction is at the nodus, where the subcosta 
ends in a transverse ridge and a furrow. The ridge adds strength to 
basal part of the wing, and the furrow gives pliancy to the wingtip, 
improving its sculling action. The nodus joins two veins (C and Sc) 
strongly to R: at the front; and subnodus (sn), oblique vein (0) and 
bridge (br) together join three principal branches (M;, Me, and Rs) 
more flexibly to it at the rear. 
(3) The basal cross connection is the most extensive one. It is 
effected by the bending to rearward of median and cubital veins at 
arculus and triangle, as already noted, and adjustment of crossveins 
to meet and support the bends. The triangle is composed of a portion 
of the cubital vein (the inner side) and two crossveins approximated 
at their front ends. Then at the hind angle of the triangle the cubitus 
is strongly joined to the anal vein. Thus strong basal braces are formed 
involving all the principal veins. 
