4oo 



MANUAL OF ELEMENTARY ZOOLOGY 



solid part, the rachis. The quill is embedded in a pit of the skin and 

 has as its lower end an opening, the inferior umbilicus, through which 

 a vascular papilla projects into the growing feather. At the junction 



of the quill and rachis is a minute 

 opening known as the superior 

 umbilicus. Close to this arises a 

 small tuft known as the aftershaft. 

 The rachis is the axis of the flat- 

 tened part of the feather, known 

 as the vexillum or vane. This is 

 composed of a series of elastic 

 plates set along the sides of the 

 rachis with their flat sides perpen- 

 dicular to the plane of the vane. 

 The plates are known as barbs, 

 and they are held together by bar- 

 bules, which are smaller processes 

 that fringe the barbs. The bar- 

 bules of one side of a barb (distal 

 barbules) bear little hooks or bar- 

 bicels which catch upon the barbules 

 of the adjoining barb. Thus the 

 whole vane is held together and 

 forms a single surface for striking 

 the air. The barbules of the 

 contour feathers are less well de- 

 veloped than those of the quill 

 feathers, so that the barbs separate 

 more easily. The filoplumes con- 

 sist each of a hair-like stem with 

 a very rudimentary vane of a few 

 isolated barbs at its apex. 



In the wing of a plucked 

 bird there may 

 easily be made 

 out parts corre- 

 sponding to the upper arm, 

 forearm, and hand. In the 

 latter the thumb is the only 



Fig. 290. — Feathers of a pigeon. 



A, Down feather; B, filoplume ; C, 

 quill feather. 



a.s„ Aftershaft ; i.u., inferior umbilicus ; 

 yw., quill or calamus ; rch., rachis or 

 shaft ; s.u., superior umbilicus; vex-., 

 vexillum or vane. 



Wings and 

 Flight. 



