OF THE CAUSES OF INTERRUPTED PLUMAGE. 17 



3. The femoral or lumbar tracts 1 (Pt. femorales seu Inmbales, Oberscbenkel- or Lenden- 



fluren). 



4. The (single or double) inferior tract (Pt. gastrcei, Unterflur). 



In a very few birds there are 



5. Lateral neck-tracts (Pt. colli laterales, Halsseitenfluren), which pass into the 



dorsal and inferior tracts. 



The other parts covered with contour-feathers would furnish the following tracts, if, from 

 their uniform feathering, they may be regarded as such. 



6. The head-tract (Pt. capitis, Kopfflur). 



7. The alar tracts (Pt. alarum, Fliigelfluren). 



8. The crural tracts (Pt. crurales, Unterschenkelfluren) ; and 



9. The caudal tract (Pt. caudee, Schwanzflur). 



II. I distinguish as spaces : 



1. The lateral neck spaces (Apt. colli later alia, Halsseitenraine). 



2. The lateral spaces of the trunk (Apt. trunci later alia, Rumpfseitenraine) . 



3. The inferior space (Apt. mesogastrai, Unterrain). 

 Besides these, the following occur more or less commonly : 



4. The spinal space (Apt. spinale, Riickgratrain). 



5. The upper wing-spaces (Apt. alee superior a, Oberen fliigelraine). 



6. The lower wing-spaces (Apt. alee inferiora, Unteren fliigelraine). 



7. The crural spaces (Apt. cruralia, Unterschenkelraine) ; and 



8. The head spaces (Apt.' capitis, Kopfrainc). 



I shall treat first of all these in general, and afterwards of each one by itself. 



CHAPTER II. 

 OF THE CAUSES or THE INTERRUPTED PLUMAGE. 



THESE must be sought on the one hand in the considerable weight of the feathers, and on 

 the other, in the bending and movements of the limbs and neck. Thus, the contour-feathers of 

 the neck and trunk, although they are usually much smaller than those of the wings and tail, are, 

 when compared with the down-feathers or hair, evidently so large and especially so broad, that 

 they cover the unevennesses and hollows of the surface of the body, fill up the differences of the 

 external outlines, and confer upon the body that smooth and rounded form which is equally 

 conducive to beauty, and to the power of flight. Nevertheless, the feathers, by their size alone, 

 would certainly obstruct, if they did not prevent, the movement and free use of the limbs, 

 especially the wings, whilst they could not render the outer surface any more uniform, if they 



' The plural indicates that the tracts are in pairs or double. 



