12 



THE BUTTERFLIES OF THE BRITISH ISLES. 



Swallow-tail butterfly. The point of attachment with the thorax 

 is the base of the wing, and the edge farthest from the base is 

 the outer margin (tertnen) ; the upper edge, or front margin, is 

 the costa ; and the lower edge is the inner margin (dorsum). The 

 point where the upper margin meets the outer margin on the 

 fore wing is the apex, but on the hind wing it is called the outer 

 angle ; the angle formed by the junction of outer and inner 

 margins is the inner angle of the fore wing, but the anal angle of 



tad 



l/ouriaL angle. 



Fig. 9. 

 Butterflies' "Wings. 



the hind wing. The term tornus is sometimes used for this 

 angle on either wing. Dividing the wings transversely into 

 three portions, we have three areas, termed respectively basal, 

 central or discal, and outer. These are terms used in descrip- 

 tions of butterflies, and it will be useful to remember them. 



The ribs of a butterfly's wings are by some authors described 

 as veins, whilst others style the main ones nervures, and the 

 branches nervules. Fig. 9, B, represents the venation, or 

 neuration of the Black-veined White, and the numeral system 



