I30 



GENERAL ORNITHOLOGY 



and vXrj, liyle, a wood) ; the latter, spaces or apteria (Gr. a privative, 

 and iTT^pov) ; they mutually distinguish certain definite areas. Not 

 only are the pterylce ^nd apteria thus definite, but their size, form, 

 and arrangement mark vrhole families and even orders of birds ; so 

 that pterylosis, or the formation of the feather-tracts, becomes avail- 

 able, and is indeed found to be important, for purposes of classifi- 

 cation. Pterylography, or the description of this matter, has been 

 made a special study by the celebrated Nitzsch, vfho has laid down 

 the general plan of pterylosis which obtains in the great majority 

 of birds, as follows : 1. The spinal or dorsal tract (pteryla spinalis ; 

 Fig. 24, 1), running along the middle of the bird above from the 

 nape of the neck to the tail ; subject to great variation in width, to 

 dilation and contraction, to forking, to sending out branches, to inter- 

 ruption, etc. 2. The humeral tracts (pt. humeralis ; Lat. humerus, 



Fig. 24. — Pterylosis of Cypsdus apus, drawn by Coaes after Nitzseh ; right hand upper, left 

 hand lower, surface. 1, spinal tract; 2, humeral; 3, femoral; 4, capital; 5, alai"; 6, caudal; 

 7, crural ; 8, ventral ; 9, elEeodochon ; 10, anus. 



the shoulder, or upper-arm bone ; Fig. 24, 2), always present, one 

 on each wing ; they are narrow bands, running from the shoulder 

 obliquely backward upon the upper-arm bone, parallel with the 

 shoulder-blade. 3. The femoral tracts (pt. femorales ; Lat. femm, 

 the thigh ; Fig. 24, 3) : a similar oblique band upon the outside of 

 each thigh, but subject to great variation. 4. The ventral tract 

 {pt. ventralis ; Lat. venter, the belly ; Fig. 24, 8), which forms most 

 of the plumage on the under part of a bird, commencing at or near 

 the throat, and continued to the vent ; like the dorsal tract, it is 

 very variable, is usually bifurcate, or forked into right or left 

 halves, with a median apterium, is broad or narrow, branched, etc.; 

 thus, Nitzseh enumerates seventeen distinct modifications. The 

 foregoing are mostly isolated tracts, that is, bands nearly surrounded 

 by complementary apteria ; the following are, in general, continu- 

 ously and uniformly feathered, and thus practically equivalent to 



