84 INTRODUCTION. 



that of quadrupeds ; tliis opening is generally covered with 

 barbed feathers, more fringed than the others. 



The organ of smell, hidden in the base of the beak, has com- 

 monly only three cartilaginous cornets, which vary as to their 

 complication ; it is very sensible, although it has no sinus dug 

 into the skull. The size of the osseous openings of the nostrils 

 governs the form of the beak ; and the cartilages, membranes, 

 feathers, and other teguments, which straighten these openings, 

 nave an influence on the strength of the smell, and on the sort of 

 nourishment. 



The tongue has little muscular substance, and is sustained by 

 a production of the hyoid bone : it has but little delicacy in the 

 majority of birds. 



The feathers, as well as quills, which differ from them only in 

 size, are composed of a stem, hollow at the base, and of barbs, 

 each having others much smaller ; their tissue, their brightness, 

 their strength, and general form, vary infinitely. Touch must 

 be weak in all parts capable of it ; and as the beak is almost 

 always corneous, and possessed of little sensibility ; and the toes 

 are covered with scales on the upper side, ana with a callous 

 skin underneath : this sense must be but little efficacious in birds. 



The feathers fall sometimes twice a year. In some species, 

 the winter plumage differs from that of the summer. In general, 

 the female differs from the male, by colours less bright, and the 

 young of both sexes resemble the female ; when the adult male 

 and female are of the same colour, the young have a dress pecu- 

 liar to themselves. 



The brain of birds has the same character as that of other ver- 

 tebrated oviperous animals ; but is distinguished by a size in 

 proportion very considerable, often exceeding that of the same 

 organ in the mammalia. It is principally to tubercles, analogous 

 to the corpora striata, that the volume is referable, and not to 

 the hemispheres, which are very narrow, and without circumvo- 

 lutions. The cerebellum is large, almost destitute of lateral 

 lobes ; and almost entirely formed by the vermiform process. 



The trachea of birds has its annulations entire ; at its bifur- 

 cation is a glottis, generally furnished with peculiar muscles, and 

 named the lower larynx: it is there that is formed the voice of 

 birds ; the enormous volume of air contained in the air-vessels 

 contributes to the force of their voice, and the trachea, by its 

 various form and movements, to the modification of the voice. 

 The upper larynx, very simple, has but little to do with this. 



The face, or upper beak of birds, formed principally by the 

 inter maxillaries, is prolonged backwards into two arcades, the 

 internal of which is composed of the palatine bones, and the ex- 

 ,ternal of the maxillaries andjugals, and which are supported on 



