B I R 



B TR' 



ture of its coats, indicate the peculiar vifion of birds and the 

 kind of mtdiiim tfiey inhabit. The aqueous humour, as al- 

 ready obfi'ivcd, is extremely abundant. It pofiefies confider- 

 able refraflive efpecially pov^■er3 in the hiijhtr rcg'ons of the 

 atmolphere. The cryjlalline is remarkably flat and foft, as its 

 offices can be fo well fiipplied by the aqneous fluid in a rare 

 medium. Both the form and tl^e proportions of the humours 

 in the eyes of all birds derive great illustration from bei::g 

 compared with thofc oi fjbt-s, which, in confequc-nre of their 

 continual refideuce in fo denfe a medium as water, have thtfe 

 parts formed upon a pian the very reverfc. — Their eye is 

 flat anteriorly; the aqueous fluid finall in quantity, and of 

 confiderable coniilteuce ; and the lens fphcrical and hard, 

 more efpecially in the centre. The cormorant has the cryf- 

 talline more Ipherical than other birds, from being obliged 

 to feek its food under the water. 



The mufcUs for the motion of the eye -ball are fix in birds, 

 as in the hum.an fubieC^ ; the four ftraight and two oblique. 

 The tendons of the recti cannot be traced farther than the 

 circle of imbiicated bones. The operation of the ftraigi.t 

 mufcles, when aiftiiig together upon the figure of the eye 

 (which, as already oblerved, is fo ftriking in birds), depends 

 upon the bony fcales of the anterior part of the fcltrotic, 

 and the thinnefs a?id pliability of that tunic pofteriorly. 

 The fuperior oblique mufcle does not pafs through a 

 pulley. 



The external eye-Ihh are chiefly clofed in birds by the ele- 

 vation of the lower one, although there is an orbicular 

 mufcle which furrounds both. The inferior eye-lid is 

 larger and thicker than the other, and contains internally an 

 oval cartilaginous plate, under which the fibres of the oibi- 

 cularis palpebrarum pafs. There is alfo a peculiar mufcle, 

 ■which comes from the floor of the orbit, and afts as a dc- 

 prejfor of the inferior eye-lid. 



The irdernal eye-lid, or memhrana n'tBltans, is a thin femi- 

 tranfpartnt membrane, which lies clofe to the globe of the 

 eye. It has a vertical pofition, and, when not employed, 

 is folded back by viitue of its own elafticity, and remains 

 concealed from view in the corner of the eye next the nofe. 

 It is, however, capable of being fpread over the whole of the 

 antciior part of the organ, by means of the combined aclion 

 of two curioufly contrived mufcles. One of them is of a fquare 

 figure, and thence called qiiadratus ; it arifes from the upper 

 and back part of the eye-ball, and approaciiing the optic 

 nerve, tcrmiiintcs abruptly in a circular edge, which con- 

 tains a pulley for the paflage of the tendon of the pyramida- 

 lis. Tliis m.iifclc ar'fes from the fide of the fclerotic next 

 the nofe a httle inferioiiy, and produces a fine tendon, 

 which runs th.rough the pulley formed in the free edge of 

 the quadratus, and afterwards returns in a cellular flieath on 

 the lower furface oi the fclerotic, and becomes attached to 

 the margin r-f the membrana niftitans, along which it is 

 continvitd for fome way, and gradually lofl:. 



The /^/tT_)'«(7/_f/««(/ is fmall in moft birds. The ghmdula 

 harderi exilts, and is larger than the lacrymal. Cuvicr de- 

 fcribes it as being gererally fituated between the addnftor 

 and levator muicles, and as having a fingk excretory duft, 

 which perforates the membrana nifiitans, and dileharges 

 upon its inner furface a yellow tenacious fluid. Many water 

 birds have a hard granular body placed at the fuperior part 

 of the orbit, which fecms to perform the office of a lacry- 

 mal gland ; and although its excretory duds have not been 

 yet feen, it probably fur.iifhes a fluid of a peculiar nature, 

 forthc detrnce of the eye againit the tfleCls of the water and 

 other accid'ut* to which aquatic birds are expofed. 



Tlie figures, wiiich ftrve to explain the organization of 

 the eye, are found in F/ateXl. oi \.ht Anatomy o/Birdj. Fig. I. 



flicws the cornea and imbricated bony fcales oV the goofe, as 

 an example of the figure thcfe parts coir.nronly aflnmc ia 

 birds. Fi^. 2. repreknts the fame parts in the horned otul, 

 in which tlie cornea will be feen very prominent, and the 

 fcales greatly elongated, forming the fore part of the e\e 

 into a tube. Fig. 3. exhibits a lateral view of the cryfl:al- 

 hne lens and the plicated membrane in the goofe's eye ; a the 

 peften attached to the pofl:erior part of the lens a little to one 

 fide ; b the edge of the lens marked by the ciliary proceflfes; 

 f the anterior part, which is particularly flat in birds. Fig, 

 4. fliews the peften and the lens in the relative fituation 

 they hold in the «ye of the turkey ; a the p icrted mem- 

 brane ; b the lens ; c the outline of the eye ; d the optic 

 nerve. Fig. 5. is a feftion of the eye of the emeu ; aa the 

 cut edges of the fclerotic coat ; bb the edges of the cho- 

 roides ; c the retina ; rf the plicated membrane fornicd liki 

 a piufe. Fig. 6. prtfeiito the anterior part of the eye of the 

 cajfjnjjary, with the membrana niditans partially drawn over 

 it, which is fo fine a film that the parts of the eye are feen 

 through it. Fig. 7. is tlie pofterior view of the caj^ozuary's 

 eye, all the mufclcs, &c. being removed, but thofe for mov- 

 ing the membrana nictitans : a the mufculus quadratus ; b 

 the pyramidalis at its origin ; c its tendon paflhig llirough 

 the pulley in the edge of the quadratus ; d the tendon pro- 

 ceeding on the fclerotic coat. 



Organ of Voics. 



Until within thefe late years this part of the anatomy of 

 birds has been involved in obfcurity. Although feveral of the 

 older anatomills defcribed the (IruCiurc by which birds pro- 

 duce found, they were ignorant of its ufes, from being 

 mifled by analogy, and fappofing that this organ occupied 

 the fame fituation in all animals. Even fome of the defcrip- 

 tions of the able!): of the modern anatomills have been er- 

 roneous or imperfeil. The fubjeft has been moll labori- 

 oufly and ingenioufly invelligated by Cuvicr. He diflisfted 

 the organs of voice ot more tlian one hundred and fixty fpe- 

 cies of bird?, and pubii(licd the refult of his inquiries in two 

 memoirs ; the principal one will be found in the Magszin 

 Encyclopcdique, torn. 2, to which we would refer the 

 reader for numerous and minute details, that would he bur- 

 thenfcm.e to introduce into the prcfcnt work. 



The true feat of the organ of voice in birds is at the bifurca- 

 tion of the trachea, and not, as geneial analogy would diftate, 

 at the fuperior larynx, which is iu birds littJe m.ore than a Am- 

 ple rima, or flit, formed, however, with fomewhat differently 

 (haped cartilages than belong to th.e refl: of the trachea, 

 and furniflicd with mufcles for opening and clofing the aper- 

 ture. The mechanilm of the inferiDr larynx, wliich fits it 

 for the prodnftion of found, depends upon the figure of its 

 cartilages, and the expanlion of its mcmbranou'5 parts. 



The two branches of the bronchia are ccmpufed of fcmi- 

 rings of cartilage ; the iuterutl furfaces, or thofe oppofed 

 to each other, being mem.branous. The femi-rings next 

 the trachea are often large, and always Itfs curved than thofe 

 near the lungs. The conlequence of which is, that the 

 membranous part of the bronchix becomes expanded in pro- 

 portion to its diilance from the lungs, and towards the bi- 

 furcation ufually aflumes an oval figure, to which Cuvierhas 

 given the name of the tympaniform membrane. 



Where the bronchia: open into the trachea, there is the 

 appearance internally of the reed ot a mufical iiiftrument. 

 This is produced by a thin and clalfic fold ol the inner mem- 

 brane, which projects upwards from each fide. The aper- 

 ture is divided into two, fomctimes by an ofTeous bar extend- 

 ed acrofs from before backwards, and iometimcs ncrcly by 

 the angle produced by the union of the two bronchis. 



When the air is expelled from the iuiigs and ;;ir-cclls with 



force 



