PLUMAGE OF BIRDS. 



237 



is a partial and temporary one, consisting of fasciculi of long fila- 

 ments of down, which on their first appearance are enveloped in 

 a thin sheath, but this soon crumbles away after being exposed to 

 the atmosphere. The down-fasciculi, which diverge each from a 

 small quill, are succeeded by the feathers, which they guide as it 

 were through the skin ; and after the first plumage, at each suc- 

 ceeding moult, the old feathers serve as the ^gubernacula' to those 

 which are to follow. It is to be observed that feathers do not grow 

 equally from every part of a surface of a bird; they are not 

 developed, for example, at those parts which are subject to friction 

 from the movements of the wings and legs. They first appear in 

 clumps upon the parts of the skin which are least affected thereby, 

 as, e. g., upon the head, along the spine, upon the exterior surface 

 of the extremities, at the sides of the projecting sternum and of 

 the abdomen. 



113 



Young Blaclihirds, showing primary down and growing featlier-clunuis. xx. 



In fig. 113, Hunter^ designates them as follows: a, ^cranial 

 clump ' {jpteryla capitis, Nitzsch) ; h, * posterior cervical ' and 

 'dorsal clumps ' (/;^. spinalis^ N.) ; d, 'lumbar clumps ' {pt.femorales 

 seu lumbales, N.); e, 'brachial clumps' (7?^. humerales, N.); /, 

 ' antibrachial,' and g, 'carpal clumps' (7;^. alarum, N.); q, 

 ' femoral clumps ' (7;^. crurales, N.) ; n, the ' anterior cervical,' and 

 o, ' pectoral clumps ' {pt. colli later ales, N.) ; 7?, ' abdominal clumps ' 

 (^pt. gastrm, N.), &c. Nitzsch^ illustrates the affinities of Birds 

 by the characters of the ' pterylae,' exhaustively followed out in 



LIV. 



The matrix, or organ by which the perfect feather is produced, 

 has the form of an elongated cylindrical cone, and consists of a 



' XX, vol. iii. p. 311. ^ Liv. 



