STRUCTURE OF BIRDS. 



69 



the neck ; a broader line from the fore part of the sternum to 

 the vent ; a space upon the sides under the wings ; and in 

 female birds, and frequently in males also, during incubation, 

 two circular spaces, or one transversely oblong space, of greater 

 or less size, upon the abdomen. Other parts also occur in par- 

 ticular species or genera, which w^ill become the subject of dis- 

 tinct consideration in their own place. 



A feather, Figs. 17, 20, may be defined an indivi- 

 dual constituent of the plumage, having a distinct 

 existence of its own, and by its association with 

 fjL others contributing to form the general envelope ; 

 \ or, in another sense, it may be defined, a mass of in- 

 lurated albuminous matter, inserted by one extre- 

 mity into the skin, connected by apposition in the 

 greater part of its extent with others, and in a por- 

 tion of one of its terminal surfaces touching the air, 

 having a root or proximal part, of a tubular form, 

 continued into an elongated and attenuated stem, 

 laterally giving insertion to a series of connected fila- 

 ments. A feather of the ordinary kind, or what may 

 be assumed as a perfect feather, consists of the fol- 

 lowing parts : 



1. The tube or barrel, Fig. 17, «, is the tubular 

 part, by which it is fixed into the skin. It consists 

 of a thinnish transparent tube or hollow cylinder, 

 having the colour and texture of a thin plate of clear horn, 

 and being chemically of the same nature. This tube, which is 

 more or less protracted, being in some feathers scarcely a 

 fortieth part of their length, as in the hypochondrial feathers 

 of Paradisea apoda, while in others it exceeds a third, as 

 in the quill-covers of the Flamingo, is abruptly narrowed 

 at the lower, or, with reference to the connection of the 

 feather with the skin, the proximal end, where it is closed 

 up by a dry membrane, forming part of an apparatus that 

 has been subservient to the growth of the other parts of the 

 feather, and which now, in a dry and shrivelled state, ex- 

 tends along the whole length of the tube, in its interior. 

 This part, when taken out of the tube of the feather, presents 



Fig. 17. 



