IGO 



AYES. 



of Piirds is formed ; the enormous volume cf air contained in the air-cavities contri- 

 butes to the stvcngtli of this voice, and tlie trachea, by its various forms and move- 

 ments, to its intonations. The vpper larynx, which is extremely simple, has little to 

 do with it. 



I'he face, or upper mandible of Birds, formed principally bjr the intermaxillaries, is 

 prolonged backwards into two arcadi'S, the internal of "which is composed by the jjala- 

 tiiie and pterygoid hones, the external hy the maxillaries and jugals, and which are 

 buth supported on a moveable tympanic bone, commoidy termed the square boiic 

 (OS cam' ), that represents the dnnn of the ear : above, this same face is articulated or 

 united to the skull by elastic lamina? ; a mode of union which always leaves some 

 mobility. 



The horny substance which invests the two mandibles supplies the place of teeth, 

 and is occasionally serrated, so as to represent them.* Its form, as also that of the 

 niandiljlcs wliich supjiort it, varies excessively, according to the sort of food 

 resorted to. 



The digestion of Birds is in proportion to the energy of their vitality, and the 

 amount of respiration. The stomach is composed of three parts : the craw, which is 

 an expansion of the gullet ; the proventriciihis, a membranous stomach, furnished in 

 the thickness of its coats with a multitude of glands [variouslj- disposed and shaped in 

 different groups], the secretion of which humects the aliment; and lastly, the 

 gizzard, armed with two powerful muscles united by two radiating tendons, and inter- 

 nally lined hy a coating of cartilage. The food is more readily ground there, as Birds 

 are in tlie habit of swallowing small stones to augment its triturating power. 



In the gTcater number of species which subsist only on flesh or fish, the muscles 

 and tlic internal lining of the gizzard are reduced to extreme tenuity, so that it apjjcars 

 to make but one sac with the proventriculus. [The same is noticeable in the Bustards, 



which subsist mainly upon herbage ; a series of inter- 

 mediate gradations, however, occurring from these to 

 the most powerfully muscular gizzards.] 



The dilatation of the craw is also sometimes [even 

 generally] wanting. [This is is commonly situate 

 above the fureula, but in the genus Palamedea 

 beyond it : in the Grebes, there is a contraction and 

 intervening space between the proventriculus and 

 gizzard t, which in the very peculiar genus Opistlio- 

 "jlF comiis is developed into a considerable cavity (this bird 

 subsisting mainly on green foliage) : the Totipahnati 

 have generally an accessory pouch to the stomach, 

 analogous to that of the Loricated Reptiles. It may 

 also be mentioned here, that in the Parrots and 

 Pigeons, both exclusively vegetable feeders, the craw 

 FiE.7o.~PiBcoi,sCraw. j^ funiislicd with numerous glands, which become 



developed in both sexes during the period that they alternately perform the duty 



i - ■ 



t,*,\ ' ■' ~<^- fitly; 



• iSee note (o p.;jft ~Ed 

 i TllL■^:,m.■CM,.tr^etiun 



iccuUle, to II le; 



I till tliey hnve Itee 

 ic Juiuc i-lal,ur,ilt-d i 



