328 



SYSTEMATIC ZOOLOGY 



feathers beneath. The contour feathers are not generally dis- 

 tributed evenly over the whole body, but are attached only on 

 certain areas called the feather tracts (Fig. 330). Some of the 

 larger feathers have special names, particularly on the wings 

 and tail. Thus the largest feathers on the wing are known as 

 remiges, and these are divided into three groups : those attached 

 to the hand are the primaries, those on the forearm are the 

 secondaries, and the three secondaries nearest the body are 

 called the tertiaries. The primaries are usually ten in number; 

 the secondaries are variable. Further, the remiges are overlaid 



B 



FIG. 330. Columba livia, the pigeon ; pterylosis. A, ventral aspect; H. dorsal, al.pt, alar 

 pteryla or wing tract; c.pt, cephalic pteryla "i head tract; cd.pt, caudal pteryla or tail 

 tract; cr.pt, crural pteryla; cv.apt, cervical apterium or neck space; fm.pt, femoral 

 pteryla; hu.pt, humeral pteryla; lat.apt, lateral apterium, sp.pt, spinal pteryla; 7 -.apt, ven- 

 tral apterium ; v.pt, ventral pteryla. (After Nitsche, from Parker and Haswell's Manual.) 



both above and below at their attached ends by smaller feathers 

 which are called respectively the upper and under wing coverts 

 (Fig. 331). The largest feathers of the tail are called rectrices, 

 as they are used in steering in the flying birds. They are also 

 provided with coverts, which sometimes are very highly devel- 

 oped, as in the tail of the peacock. 



The skin of birds is destitute of glands except for one found 

 on the dorsal side of the base of the tail ; it is an oil gland, 

 called the uropygial gland, and its secretion serves to oil the 

 feathers. Other epidermal structures, besides the feathers, 



