THE PIGEON 



401 



digit that projects. A fold of skin known as the pro- 

 patagium connects the shoulder with the forearm in front, 

 and a small postpatagium of the same kind lies across 

 the armpit. The greater part of the surface of the wing, 

 however, is provided by the row of twenty-three remiges 

 along the hinderside of the limb. The remiges borne 

 upon the hand are eleven in number and are known as 

 primaries. These on the forearm are known as secondaries. 



ABB 



Fig. 291. — Parts of a feather. — After Nitzsch. 



/., Four barbs (B.) bearing anterior barbules (A.BB.) and posterior 

 barbules (P.BB.) ; //., six barbs (B.) in section } showing inter- 

 locking ofbarbules ; ///., anterior barbule with barbicels (//.). 



A tuft of feathers on the thumb is the bastard wing. In 

 flight the wing strikes downwards and forwards, twisting upon 

 its axis with a screw action which has the result of driving 

 the body forwards while it holds it up. In rising the angle 

 is altered and the wing strikes more downwards. In gliding 

 to the ground the wings are outspread and serve to check 

 the fall. The tail feathers can be spread out on one or both 

 sides, and are used for steering and to check the " way " of 

 the bird, as in alighting. The downstroke of the wing is 



