nPteryla(Zoöl) One of the definite areas of the skin of a bird on which feathers grow; -- contrasted with apteria.
Century Dictionary and Cyclopedia
npterylaA feather-tract; one of the sets or clumps of feathers which are inserted in definite tracts or areas in the skin of a bird, separated by apteria, or places where no feathers grow. The fact that birds' feathers are seldom implanted uniformly over the whole skin, but usually grow in definite patches, had been known long before the publication of Nitzsch's “System of Pterylography” in 1840; but it remained for this author to define the principal pterylæ and point out the taxonomic significance of pterylosis. The most constant pterylæ are eight: Pteryla spinalis, the spinal or dorsal tract, from the nape of the neck to the tail, subject to much modification.