90 



GENERAL ORNITHOLOGY. 



spinal or dorsal tract (pteryla spinalis ; fig. 24, 1), running along the middle of a bird above 

 from nape of neck to tail ; subject to great variation in width, to dilation and contraction, to 

 forking, to sending out branches, to interruption, to enclosing an apterium, etc. 2. Humeral 

 or arm tracts (pt. humerales ; Lat. humerus, shoulder, or upper arm-bone; fig. 24, 2), always 

 present, one on each wing ; they are narrow bands, running from the shoulder obliquely back- 

 ward upon the upper arui-bone, parallel with the shoulder-blade. 3. Femoral or thigh tracts 

 (pt. femorales ; Lat. femur, thigh; fig. 24, 3) ; a similar oblique band upon the outside of each 

 thigh, subject to great vaiiation. 4. The ventral tract (pt. ventralis ; Lat. venter, belly ; 

 fig. 24, 8), which forms most of the plumage on the under part of a bird, commencing at or 

 near the throat, and continuing to the vent ; like the dorsal tract, it is very variable, is broad 

 or narrow, branched, etc., though always consisting of right and left halves, with a median 

 apterium ; thus, Nitzsch enumerates seventeen distinct modifications, and there are others. The 

 foregoing are mostly isolated tracts, that is, bands nearly surrounded by complementary apteria ; 

 the following are, in general, continuously and uniformly feathered, and thus practically equiva- 

 lent to the part of the body they represent : Thus, 5, the head tract {pt. capitalis ; Lat. caput. 



Fio. 24. — Pterylosis of Micropus apus, drawn by Cones after Nitzsch ; right hand upper, left hand lower, surface. 

 1. spinal tract; 2. humeral; 3. femoral; 4. capital; 5. alar; G. caudal; 7. crural; 8. veutral. 



capiitis, head ; fig. 24, 4) clothes the head, and generally runs into the beginning of both dorsal 

 and ventral tracts. 6. There may be a recognizable neck tract (pt. colli ; Lat. colliitn, neck), 

 and in some cases, as Herons, what Nitzsch called pt. colli laterales. 7. The alar or wing tract 

 (pt. alaris; Lat. ala, wing; fig. 24, 5) represents all feathers that grow upon the wing, ex- 

 cepting those of the humeral tract. 8. The caudal or tail tract {pt. caudalis; Lat. cauda, tail; 

 fig. 24, 6) includes the tail-feathers proper and their coverts, and usually receives the termina- 

 tion of dorsal, ventral, and femoral tracts. 9. The crural or leg tract {pt. cruralis ; Lat. crits, 

 cruris, leg; figs. 24, 7) clothes the legs as far as these are feathered, which is generally to the 

 heel, always below the knee, and sometimes to the toes or even the claws. 10. The uropygial 

 or rump tract (pt. uropygii) is confined to the elaeodochon, which may be uniformly feathered, 

 or naked except for a peculiar circlet of feathers which surmounts it. I need not enumerate the 

 apteria, as these are merely the complements of the pterylae. The highly important special 

 " flight-feathers" of the wings and " rudder-feathers " of the tail are to be examined beyond, 

 in describing those members for purposes of classification. 



Endysis and Ecdysis. — Putting on and off Plumage. — Newly hatched birds, as 

 already said, are partially or entirely covered for some time with a kind of down neossop- 

 tiles, entirely difi"erent from such teleoptiles as they ultimately acquire. The relation 



