THE SKIN AND ITS APPENDAGES 105 



of the feathers. Bundles 

 of muscle - fibres are so 

 arranged that their con- 

 traction erects the 

 feathers. For the most 

 part the corium or der- 

 mis of the skin is not 

 very vascular, the comb 

 and wattles, however, 

 forming an exception. 



Feathers are epidermic 

 structures partly embed- 

 ded in follicles of the skin. 

 A typical feather (Fig. 

 52) consists of an axis 

 or scapus and a vexillum 

 or vane. The lower part 

 of the axis is known as 

 the calamus or quill, and 

 is rounded, transparent, 

 and hollow, with a series 

 of conical scales in its in- 

 terior. At the end of 

 the quill is a small open- 

 ing, the inferior umbili- 

 cus, into which projected 

 a papilla of the dermis 



bb. -^ 



ca^ 



I.U.- 



Fig. 52.— 

 Diagram of 

 the Parts of 

 a Feather. 



v., vexillum; b., barb; bb., bar- 

 bules ; r., rhachis ; h., hyporhachis ; 

 S.U., superior umbilicus; cal., cala- 

 mus ; i.u.j inferior umbilicus. 



