66 AVES. 



structures beneath. Occasionally the feathers assume a hair-like 

 character, as upon the eyelids and base of the bill, e. g. in the Ra- 

 ven. It is very rarely that true hairs resembling bristles are met 

 with, as upon the neck of the Turkey. 



The epidermic plant-like horny structures of Birds, the Feathers, 

 are divided into Down-feathers and Contour or Quill-feathers. The 

 first are delicately soft and flexible, mostly of a gray or grayish-yel- 

 low color, and lie beneath obscured by the quill-feathers. There are 

 feathers which are entirely downy, but each quill-feather, even the 

 large primaries of the wing, has some strips of down at its com- 

 mencement. The feathers of the neck and trunk form in most Birds 

 circumscribed patches (pteryla), which are distinctly defined by 

 means either of intervals naked or beset with down. 



In a perfectly formed Feather, the following parts may be distin- 

 guished. 1st. The stem (scapus), which forms the principal part of 

 the feather ; it is cylindrical or fusiform, and is prolonged inferiorly 

 into the transparent hollow part, the quill (calamus), by which it is 

 attached to the skin. Within the quill is found what is called the 

 pith, which consists of membranous cones arranged one upon the 

 other. Externally, where the vane or beard of the feather commen- 

 ces, the stem becomes medullary, and is then called the Shaft (ra- 

 chis). This shaft, over the back of which the quill is continued as 

 a horny investment, is almost always quadrangular, and rarely quite 

 flat, as in Aptenodytes. The inferior surface of the shaft, namely, 

 that which is turned toward the body of the bird, is hollowed out 

 into a groove, and is depressed at the commencement of the quill 

 into an umbilical fossa, near or from which the accessory plume 

 (Jiyporhachis) arises. This resembles the main shaft, in giving off 

 a bilinear series of barbs, and the two together form an apparently 

 double feather. It is wanting in the primary feathers of the wing 

 and tail. It frequently supports merely downy barbs, as in the Gal- 

 linse, and is occasionally reduced to a single barb, or is wanting al- 

 together, as in the Owls, many Picarise (Alcedo, Upupa), and Ducks, 

 &c. From either side of the main and accessory plumes arise 

 the Barbs which form the vane (yexillum) of the feather. They are 

 small lancet-shaped lamella, varying in form, length, and thickness, 

 in different Birds. In like manner, from either side of the barbs, 

 proceed the Barbules (radii}, which are much more numerous and 

 complex in their structure than the barbs. Occasionally, like as in 

 a tripinnate leaf, the barbules are provided again with smaller 

 accessory barbules, constituting a third series. The barbules are 



