EXTERNAL PARTS OF BIRDS. — FEATHERS. 8/ 



cpvtaiu birds, as the ostrich tribe, penguins, aud toucaus. If we compare a bird's skin to a 

 well-kept park, part wooiUand, part lawu ; theu where feathers grow is the wnodlainl ; wlirre 

 they do not grow is the lawu. The forua^r places are called tractf: or ptfnjlcc (diuiiu. frum Gr. 

 TrTtpdi", pterOH, a plume) ; the latter, .spaces or apteria [Gr. a privative, aud Trrepop) ; they 

 mutually distiugiush certaiu defiuite areas. Not ouly are the pterijUe and apteria thus defiuite, 

 hut their size, form, and arrangeuieut mark whole families aud even orders of birds ; so that 

 pterylosis becomes available, and is indeed found to be important, for purjioses of classification. 

 Pterijlographii, or the description of this matter, has been made a special study by tlie cele- 

 brated Nitzsch, who has laid down the general plan of pterylosis which obtains in the great 

 UKijority of birds, as follows: 1. The spinal or dorsal tract (pteri/la S2)inalis; fig. ii, 1). 

 running along the midiUc 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 

 interruption, etc. 2. The humeral tracts (pt. hnmcrale.': : Lat. liiimerus, the shoulder, or upper 

 arm-bone: fig. 2i, 2), always present, one on eacli wing: they are narrow bauds, running from 

 the shoulder obUquely backward upon the upper arm-bone, parallel with the shoidder-blade. 



Fk-,. 24. — Pterylosis of Cijpse/ii..^ aj>u.<. di\iwn by Cones .ifter Xitzsch; riglit hiind upper, left lian.l lowe 

 if;K'e. 1. spinal tract; 2. humeral; 3. femoral; 4. capital; 5. alar; 6. caudal; 7. crural; S. ventral. 



•S. The femonU tracts (pt. fiiiiorales : Lat. femur, the thigh: tig. ii, 3): a similar oblique 

 band upou the outside of each thigh, but subject to great variation, i. The ventral tract {j>t. 

 fentralis ; Lat. renter, the belly : tig. 2i, S), which forms most of the ]dumage on the under 

 part, of a bird, comnienciug at ur 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 medi;in 

 apterium, is broad or narrow, branched, etc.; thus, Xitzsch enumerates .■iereiifeeii distinct modi- 

 fications ! The foregoing are mostly isolated tracts, that is. bands nearly surrounded bv com- 

 plementtiry apteria ; the following are, in general, continuously aud uniformly feathered, and 

 thus practically equivalent to the part, of the body they represent : Thus, 5, the head tract 

 (2]t. ccipiitali.'i : Lat. capnt. capitis, head ; fig. rii, 4) clothes the head, and generally runs 

 into the beginning 'of both dorsal and ventral tracts. 6. The wing tract (pt. alari.i : Lat. (i/((. 

 wing : fig. -Ji, .5) represents all the feathers that grow upon the wiiio. exceptino- those of 

 the humenil tract. 7. The tail tract (jjf. ctiadalix : Lat. C(Y»(/(7, tail : fig. -ii. (i i includes 

 the tail-feathers proper aud their coverts, and those about the ekcodoclinii. and usually receives 

 the termination of the dorsal, ventral, and femoral tracts. S. The leg tract (jit. crurali.'.- : 

 Lat. cms, cruris, leg ; figs. 2i, 7) clothes the leas as far as these are feathered, which is 

 generally to the heel, always below the knee, aud sometimes to tlie tiies or even the claws. — 

 I need not enumerate the ajjteria. as these are merely the complements of the ptervhe. The 



