231 



CHAPTER XXII. 



TEGUMENTAEY SYSTEM OF BIRDS. 



§ 164. Composition of the Tegument. — This is composed, as in 

 Mammalia and Reptilia, of the corium or derm, the epiderm and 

 its appendages, and an intermediate layer of unhardened epiderm 

 with colouring matter, called ' rete mucosum.' 



The corium, or true skin, is very thin and lacerable, but vascular. 

 In some Birds it adheres to the subcutaneous muscles by cellular 

 tissue, Avhich is frequently the seat of accumulation of dense 

 yellow fat. In the Penguin the layer of subcutaneous cellular 

 tissue adheres to the corium, but is separated from the muscles, 

 and has a smooth internal surface: long vessels, like threads, 

 connect this layer to the muscles. The skin is moved by muscles 

 which at the same time raise and ruffle the plumage which it 

 supports. In most Birds the skin is more or less separated from the 

 muscles of the trunk by the interposed air-cells ; as in the Batra- 

 chians it is by the lymph receptacles. It adheres, however, to a 

 larger proportion of the osseous system than in other classes ; as, 

 e. g., to the upper and lower jaws, the feet and part of the tibije, 

 the pinion bones. The corium has extensions beyond the covering 

 of the body, to form the webs for swimming and the broader folds 

 at the axilljB and bend of the arm for flight : it developes the 

 papilla? beneath the toes, the vascular comb and wattles of the 

 Cock, the caruncle and pendent ornaments of the Turkey, &c. 



The rete mucosum rarely contains any colouring matter where 

 the feathers grow ; at this part the skin is of a pale greyish colour, 

 or pink, from the colour of the blood which circulates in it. But 

 in the naked parts of the integument, as the cire, the lore, the 

 comb, the wattles, the naked parts of the head and neck in some 

 Birds, and the tarsi and toes, the rete mucosum frequently glows 

 with the richest crimson, orange, purple, green, black, and a variety 

 of other tints, of which the planches colorices and the different 

 zoological monographs of geographical groups and families of Birds 

 afford numerous examples.^ 



* Amongst these merit highest mention the works of our countryman Gould on 

 the Birds of Australia, Europe, Asia, Great Britain, &c.; and his magnificent mono- 

 graphs on the Humming-Birds, Trogons, and Toucans. 



