1 66 ELEMENTS OF OENITHOLOGfr, 



kinds of birds, sending out branches, bifurcating or suffering 

 interruption, as the case may be. Fig. 147 (i). 



The ventral pteryla extends from the throat to the root 

 of the tail, and may vary in disposition, as already stated, with 

 respect to the dorsal pteryla. Fig. 146 (8). 



The cranial pteryla, or tract of the head, more or less 

 extensively invests the head and becomes continuous with the 

 dorsal pteryla. (4). 



The caudal pteryla, or tail-tract, comprises both the dorsal 

 and ventral surface of the tail, wherein the rectrices and upper 

 and lower coverts are inserted. (6). 



The hjimeral pterylae, or shoulder-tracts, are constant but 

 small. One crosses obliquely backwards and inwards over the 

 shoulder from the upper part of the upper arm. Fig. 147 (2). 



The alar pterylse, or wing-tracts, run each along the soUd 

 part of one of the wings from the upper arm to the end of the 

 pinion. (5). 



The femoral pterylae, or thigh -tracts, form two oblique bands, 

 one outside either side. They are very variable. Fig. 147 (3). 



The crural pterylse, or leg-tracts, cover those portions of 

 the pelvic limb below the knee which have feathers inserted 

 into them. (7). 



Downy feathers generally clothe the body (partially or en- 

 tirely) independently of the pterylse, and beneath the other 

 feathers distinguished as contour feathers. But down may be 

 absent altogether, as in the Woodpeckers. 



