THE FEATHERS 399 



ii. The rectriees, or tail-quills, have the two halves 

 of the vane about equal in size. They are 

 used by the bird for steering during flight. 



They are twelve in number in the wild 

 rock-pigeon, but vary in domestic breeds. 

 }}. The coverts are the smaller feathers which cover the 

 bases of the quills of the wings and tail. 



c. The contour feathers are the short soft feathers 



covering the body generally. The barbules are 

 less perfectly developed than in the quill-feathers, 

 so that the barbs readily separate from one an- 

 other, especially at the base of the vane. 



d. The filoplumes are the minute rudimentary feathers 



left in the skin after the bird has been plucked. 

 Each consists of a hair-like stem, with a very 

 rudimentary vane at its apex. 



3. Arrangement of the feathers. 



The feathers are attached to certain definite areas 

 of the skin, known as pterylae, the intervening tracts 

 or apteria being devoid of feathers. This arrange- 

 ment is not very obvious in the pigeon, in which the 

 feathers are more uniformly distributed than in 

 many birds. Apteria may, however, be seen in the 

 mid-ventral and mid-dorsal regions of the body, and 

 along the outer surfaces of the proximal segments of 

 the wings. 



D. External Apertures. 



a. Median apertures. 



i. The mouth is a wide slit-like opening in the long 

 pointed beak. 



ii. The cloacal aperture is a transverse slit, with 

 prominent Hps, on the ventral surface of the 

 body, below the base of the tail. 



b. Paired apertures. 



i. The nostrils are a pair of oblique slit-like 

 apertures, between the beak and the cere. 



