. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. INTEGUMENT. 23 Palseontological researches have not yet brought to light any definite inter- mediate stages between scales and feathers, but that they must once have existed is shown by the development of these structures (comp. Fig. 12 and description). There is no trace of proper dermal bones (derinostoses)l or calcifications in the skin of Birds, and the glands are reduced to a single mass—the uropygial gland: this is situated at the base of the tail (uropygium), and its secretion serves to o
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. INTEGUMENT. 23 Palseontological researches have not yet brought to light any definite inter- mediate stages between scales and feathers, but that they must once have existed is shown by the development of these structures (comp. Fig. 12 and description). There is no trace of proper dermal bones (derinostoses)l or calcifications in the skin of Birds, and the glands are reduced to a single mass—the uropygial gland: this is situated at the base of the tail (uropygium), and its secretion serves to oil the feathers. Epidermic structures, such as claws, spurs, foot-scales, and beak-sheaths, are strongly developed. A < i~ B. G STAGES IN THE DEVELOPMENT OF HAIR. St., stratum corneum ; SM, stratum Malpighii; C, derma; F, follicle ; I)r sebaceous c-land ; CZ, central, and PZ, peripheral zone of the hair-germ ; HK, hair-knob ; P, beginning of the formation of the hair-papilla ; P>, the same in a later stage of development, when it has become vascular. Mammals.—The hair-like structures possessed by certain Reptiles and Birds are historically quite distinct from the true hairs of Mammals. The possession of hairs characterises Mammals quite as much as feathers distinguish Birds from all other animals. 1 See note on p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wiedersheim, Robert, 1848-1923; Parker, W. N. (William Newton), d. 1923. London, New York, Macmillan
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