AVES. 849 



Peculiar Secretions. The unctuous fluid the habits and manner of life of the different 

 with which Birds lubricate their feathers is orders. A remarkable artificial form is given 

 secreted by a gland which is situated above the to the claw of the middle toe in certain birds ; 

 coccyx or uropygium. This gland consists of the inner edge being produced and divided 

 two lateral moieties conjoined. As might be into small parallel processes like the close-set 

 expected, it is largest in the birds which frequent teeth of a comb (fig. 132.) These teeth are not 

 the water. In the Swan it is an inch and a reflected or recurved, as they might be expected 

 half in length, and has a central cavity, which to be, if they had been intended to serve as 

 serves as a receptacle for the accumulated secre- holders of a slippery prey, but are either placed 

 tion ; but this cavity has not been observed in at right angles to the claw or are inclined to- 

 other species. Each lateral portion is of a wards its point. The Common Barn-Owl f,Sftn\r 

 pyriforrn shape, and they are conjoined at the Jlammea), the Goat-sucker genus (Caprimul- 

 apices, which are directed backwards and are gus), the Heron and Bittern kind (Ardeidte, 

 perforated by numerous orifices. The longitu- Vig.), afford examples of this structure; and 

 dinal central cavities also present internally nu- as each species of bird appears to be infested 

 merous angular openings, in which there are by its peculiar louse (Nirmus), the solution 

 still smaller orifices. The surrounding glandu- of the final intention of so singular a con- 

 lar substance consists of close-set almost paral- trivance, which is limited to so few species, 

 lei straight tubules,and is not irregularly cellular, and these of such different habits, may yet 

 The tubules extend to the superficies of the be afforded by the entomologist. At least 

 gland, without ramify ing or intercommunicating, it would be worth while to examine the pa- 

 and preserve an equable diameter to their blind rasitic animals of the species so provided, with 

 extremities. The tubules are longest at the the view of determining whether they pos- 

 thickest part of the gland, and become shorter sessed superior powers of adhesion which 

 and shorter towards the apex. might require the application of a comb in the 



Tegumentary system. This is composed, as birds infested by them.* 



in Mammalia and lleptilia, of the corium or With respect to the scales which defend 



derm, epiderm, and its appendages, and an the naked parts of the legs of birds, they do 



intermediate layer of unhardened epiderm with not differ from those of Reptiles. Their form 



colouring matter, called rcte mucosum. and disposition, as has been already observed, 



The corium, or true skin, is very thin, as in have afforded distinctive characters to the zoo- 



the cold-blooded Ovipara. It adheres to the legist. In most of the Raptores, the Psitta- 



subcutaneous muscles by cellular tissue, which cid<e, the Rasores, the Grallatores, and the 



is frequently the seat of accumulation of dense Natatorcs, the scales are polygonal, small, 



yellow fat ; and it is moved by muscles which and disposed in a reticulate form ; the birds 



at the same time raise and ruffle the plumage so characterized formed the Retipedes of Sco- 



which it supports. poli. In the rest of the class the tarsi are 



The rete mucosum rarely contains any co- covered anteriorly with unequal semi-annular 



louring matter where the feathers grow ; at scales, ending on each side in a longitudinal 



this part the skin is of a pale, greyish colour, furrow, and these birds were termed the * Scu- 



or pink, from the colour of the blood which tipedes'-\ 



circulates in it. But in the naked parts of The four classes of vertebrate animals have 



the integument, as the cire, the lore, the each their characteristic external covering : the 



comb, the wattles, the naked parts of the head cold-blooded Ovipara are naked, or their ex- 



and neck in some birds, and the tarsi and tenial surface is defended only by hard scales 



toes, the rete mucosum frequently glows with or plates (squama and scuta) ; but the warm- 



the richest crimson, orange, purple, green, blooded classes require to be invested by an 



black, and a variety of other tints, of which integument better adapted to maintain the high 



the planches colories and the different zoological degree of temperature peculiar to them : hence 



monographs of families of birds afford nu- quadrupeds are clothed with fur and hair, and 



merous examples. birds with down and feathers. 



The epidermis is in some places continued Feathers are the most complicated of all 



as a simple layer over the corium, following the modifications of the epidermic system, 



its wrinkles and folds, as around the naked necks and are quite peculiar to the class of birds, 



of some Vultures. It is moulded upon the The eloquent Paley well observes that " every 

 bony mandibles to form the beak, and in some 



birds adheres to osseous protuberances on the .. Mr ; s t wains $&** ^ *eory which 



. f P , ascribes to the serrated claw the function of freeing: 



cranium, where it forms a species of horn; and thc p i umag e from vermin, because its presence is 



it is remarkable that these instances occur chiefly partial in the class of Birds. " To suppose," says 



in those orders of birds, the Cursores and he, " that nature has given to one or two families 



Rasores, which are most analogous to the Ru- of birds the exclusive power of freeing themselves 



minantia among quadrupeds : the Cassowary ? om a ? enemv which in like manner infests all 



ft^ nV, y birds, is preposterous." The assertion that the 



and Helmeted Curasspw are examples. The different s ^ ec ies of Nirmi infest all birds in like 



cuticle is sometimes developed into spines or manner is much easier than the proof, 



spurs, as upon the wing of the Secretary-bird, t In one section of the Tyranni, Cuv. the scuta; 



Cassowary, the Apteryx, and the Palamedea ; surround the tarsi as complete rings. Where the 



and upon the tarsi of the Gallinaceous Birds. <-arneous parts of the muscles are continued low 



rr>\ i u u ii, A.\, ii-i down upon the lees, as in the Owls, a covering of 



The claws which sheath the ungueal phalanges feather3 P is co-winded to preserve their templra- 



of the feet assume various forms adapted to ture. 



