IDENTIFICATION. 



49 



breaks off into fine dust as fast as it is formed. Sometimes these 

 feathers are scattered all over the body, but in many cases they are 

 in well defined positions which are known as " powder down tracts," 

 and these tracts are of considerable use in identifying the Herons, for 

 instance. Just as the powder down is distributed in tracts, so are the 

 contour feathers, except in the case of the Ostriches and their allies, 

 and the Penguins and a few more birds. 



That the feathers should be arranged in a definite pattern was 

 to be expected. If the body were feathered evenly it would 

 hamper the bird in its movements. The coat is in fact made 

 to fit, and is cut in such a way as to be workable by the 

 muscles. These "tracts," with their resulting spaces, which were 

 worked out by Nitzsch, are of considerable importance in ornithology, 

 and promise to be of more importance in the future ; and 



we have, in consequence, 

 given two sketches of our 

 thrush ; the first dorsal, the 

 second ventral, with the 

 chief tracts and spaces 

 marked out. 



Most birds have a spinal 

 . or dorsal tract, a humeral or 

 shoulder tract, a femoral or 

 lumbar tract, and what is 

 known as the inferior tract ; 

 some of them have a neck 

 tract ; and besides these, 

 are the head tract, the alar 

 or wing tract, the crural or 

 leg tract, and the caudal 

 tract. The spaces are the 

 laterals of the neck, the 

 laterals of the trunk, and 

 the inferior lateral ; and 

 besides these, the more or 

 less common spaces are the spinal, the upper wing, the lower wing, 

 the crural, and the head. 



The spinal tract is occasionally bordered below with a row of 

 feathers, as in the Woodpeckers. Sometimes it is weak at the nape, 

 as with the Kingfisher. In the Golden Oriole it is widened on the 

 back into an ellipse. In the Crows and Larks it has a space within 

 its boundaries. In the Woodpeckers, including the Wryneck, and in 

 the Swallows it has two lobes. In the Pheasant, the Partridge, and 

 the Quail it is well marked and continuous, and narrow on the neck, 

 but widening from the shoulder blades ; while in the Capercaillie it is 

 cleft where it broadens by a longitudinal space from the shoulders 

 upwards. On the other hand, in many birds of prey, it is interrupted 

 at the ends of the shoulder blades, the anterior part becoming wider, 

 and the lower part becoming narrower. And a further variation 

 occurs among the Plovers and Sandpipers, where the hinder part is 

 cleft throughout. 



The humeral tract, in the Passerine birds, runs nearly over the 

 middle of the humerus, but in the Pigeons it crosses much nearer the 



