16 ANIMAL BIOLOGY. [Parti. 



the upper mandible is a swollen and featherless patch of skin, 

 the cere. The cranial division of the head is well rounded. In 

 the feathered pigeon the neck passes gracefully into the body, 

 but in the plucked bird the distinction between head, neck, and 

 trunk is obvious. The body tapers backwards, the thoracic 

 region being well developed, guarded by ribs, and provided with 

 a large ventrally-keeled sternum. The feathered tail is fan- 

 shaped ; but the plucked tail is an insignificant upturned pro- 

 tuberance. There are two pairs of limbs ; the anterior converted 

 into wings, the posterior into cursorial legs. 



There is a well-developed exoskeleton consisting of feathers. 

 The beauty of form is given mainly by the contour feathers 

 (pennce), but if these be plucked there still remain the more 

 delicate plumose filoplumes. There are strong quill-feathers in 

 the wings (remiges) and in the tail (rectrices). The hues of the 

 living bird are largely due to the metallic tints of the feathers. 



Although the external appearance of the pigeon would lead 

 one to suppose that the feathers are developed uniformly over 

 the whole body, yet closer inspection shows that they are 

 arranged in more or less definite feather tracts (pterylce\ sepa- 

 rated by featherless spaces (apteria). This may be better seen 

 in a young blackbird or sparrow. There is a spinal tract along 

 the mid-line of the back, broadening or bifurcating posteriorly. 

 On the ventral surface are two parallel bands constituting the 

 ventral tract, and separated by a median inferior space. The 

 spinal and ventral tracts are separated by lateral spaces. There 

 are also special feather tracts on the wings and legs. In the 

 plucked bird, which loses by this process the characteristic grace 

 and symmetry of outline, the feather tracts may be traced by the 

 scars left by the removal of the feathers. 



A quill feather consists essentially of a proximal part (that is, 

 a part nearer the body), the quill, and a distal part (further from 

 the body), the feather or vane. The quill (calamm) is cylindrical 

 and hollow ; at its proximal end is a hole (inferior umbilicus) into 

 which a little fleshy feather-papilla is inserted ; at the distal end, 

 where the quill joins the shaft of the vane, there is an oblique 

 aperture (the superior umbilicus). The vane (vexillum) has a 



