106 THE STRUCTURE OF THE FOWL 



during the period of development of the feather. 

 About the junction of the quill and the vane 

 is another small opening, the superior umbilicus, 

 and in this region arises a small, variable tuft, 

 the aftershaft or hyporhachis. 



The axis of the vane, the rhachis, is solid, 

 four-sided, tapering, and elastic, with a longi- 

 tudinal groove running along that surface 

 which looks towards the body when the feather 

 is in position. The vane itself consists of 

 two rows of narrow, slender lamellae, or barbs, 

 springing from the rhachis and sloping obliquely 

 outwards and towards the tip of the feather. 

 Each barb, in its turn, carries two rows of 

 barbules. The barbules of the distal row, i.e. 

 those which grow from that side of the barb 

 which looks towards the tip of the feather, 

 are provided with microscopic booklets which 

 hook on to the doubled - over edge of the 

 barbules of the proximal row. By this inter- 

 locking of the barbules, the vane is converted 

 into a continuous elastic whole, capable of 

 offering the necessary resistance to the air 

 during flight. 



All the feathers of the body are not of the 

 same size or form. The largest are the remiges 

 of the wing and the rectrices of the tail. The 



