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external, inftead of pointing iiuvai-Js, as in man and qua- 

 drupeds. 



The cavity of the timpar.um is irregular on the internal 

 furface, and is widell at its outer part. Bcfidcs the ufnal 

 foramiia leading, to the labyrinth and Eiitlachian tube, it 

 contains three others, which communicate with the cells of 

 the bones of the cranium. Thcfe are widened into fome- 

 thing like canals, where the hole."! open into them. The 

 largeft of the foramina is in the back of the tympanum, ai.d 

 leads to the poilcrior cells, and communicates above the fo- 

 ramen magnum with the cellular canal of the other fide. 

 The fecond opening is placed at the anterior part oi the 

 tympanum, and condiurts to the cells on the lower and ante- 

 rior part of the cranium. The third foramen is conti'iuid 

 amongft the cells which furround the labyrinth. Tims the 

 cavities of each tympanum have a communication with the 

 interior of all parts of the cranium, and with each other, 

 from which they might be reckoned as making only one ca- 

 vity. The end of the articular bone alfo, where it con- 

 tributes to form the parietes of the tympanum, has a fora- 

 men, by which it derives its fupply of air. The audi- 

 tor\ cells of the cranium of birds are analogous to the 

 maftoid of the human fubjeft ; but from their extent, 

 multiply found much more. They are of the greateft mag- 

 nitude in the nndurnal birds of prey, and efpecially in the 

 <white oiul ; the goat fucker ( caprhnulgus) has them alfo very 

 large. They diminilh in the other birds, in which the poi- 

 teiior canals have no direft communication with each other. 

 They arc little obfervable in the flrutlAs ; and the parrot 

 appears to want them altogether, but in their place the ca- 

 vity of the tympanum is enlarged polleriorly. 



The Eujlach'ian tube is very large in birds ; it is an ofTeous 

 canal, and terminates by a fmall aperture clofe to the one of 

 the other fide, within the filTure of the pollerior nares. 



The foramina, which lead into the labyrinth, are fituated 

 within a foffa. They do not merit the dilUnctions of fora- 

 men ovale and foramen roiur.dum, being both oval, and only 

 feparated by a fmall bony procefs. 



The qfficu'a auditus are fupplied by a fingle bone and fome 

 cartilaginous procefles. The officulum confills of a ilalk or 

 pedicle, crowned by an oval plate, which is apphcd to the 

 foramen that leads into the vellibule of the labyrinth. At 

 the other extremity it becomes extended and united to two 

 or three cartilaginous procefles, which form a triangle that 

 is attached to the membrana tympani. 



The pediculated bone of the tympanum is moved by one 

 mufcle, which comes from the occiput behind the ear, and 

 penetrating the cavity, is afExed to the triangle that is con- 

 nefted to the membrana tympani. This mulcle is a tenfor, 

 and draws the membrana tympani outwards. It is counter- 

 afted by two fmall tendinous cords that are extended to the 

 internal parietes of the tympanum. 



The hibyrinth of the ear of birds confifts only of the vef- 

 t'ibule and three femic'ircular cana!:, and the rudiment of the 

 cochlea. 



The I'e/l'ibule is fmall in proportion to the other parts. 



The canals have been termed by Scarpa, from their gra- 

 dation in bulk, canales major, minor, and minimus. The 

 largeft is moft fuperior, and has a vertical pofition. The 

 fmalleft is fituated horizontally. The canalis minor afceuds 

 upon the major, and opens into its fide. They contain cor- 

 refponding tubes of vafcular membrane ; and they alfo pof- 

 fefs the ampulla, on which the nerves are diftributed in the 

 fame manner as in mammalia. 



The place of the cochlea is fupphed by a fliort offeous 

 lube, very flightly bent, and either blunt or enlarged at the 

 extremity. Its interior is occupied by two fmall cylinders 



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of fine cartilage, each a little twilled, and united at their 

 orirrin and termination. They proceed from the offeouj bar, 

 which feparates the two foramina that coriefpond to the fo- 

 ramen ovale and rotundum. The fulcus, which is left be- 

 tween the cartilages, is dilated near the point, and ac- 

 commodates the fame branch of the auditoi7 nerve which is 

 fent to the cochlea in mammalia. This nerve fpreads in fine 

 filaments upon the united extremity of the cartilaginous cy- 

 linders. The tube is divided by tlit prefence of the carti- 

 lages into two Icalx, which communicate with the veftibule 

 and the foramen rotundum. 



The fruihious birds have the tube correfponding to the 

 cochlea, very fmall in proportion to the other parts. 



The auditory mrve is received into a foffa, and there breaks 

 into five branches ; one is the facial, or portio dura, and the 

 others are fent to the femicircular canals and the tube. The . 

 facial nerve receives a filament from the par vagum, which 

 traverfes the car, and is afterwards diftributed to the palate. 



Comparetti has dcfcribcd two canals leading from the laby- 

 rinth of birds, which correfpond with the aqueducts of the 

 ear of mammalia. 



For the illuftration of th? organ of hearing, fee Plate X. 

 ill the Anatomy of Birds. Fig. 9. reprefents a difleftion of 

 the pollerior portion of the ilcuU of the it'/j/V? onxil {Jlrix 

 fammea), which expofes both the parts of the tympamira 

 and the labyrinth ; a the membrana tympani, which is iii- 

 clofed in a perfedl frame of bone in this bird ; b the cavity 

 of the tympanum laid open on the other fide of the head ; 

 c the pediculated bone, or ofiiculum, in fitu ; ddd the fe- 

 circular canals ; e the tube analogous to the cochlea ; // 

 the air-cells expofed by the divifion of the cranium. Fig. 

 10. fnews the olTiculum and the membrana tympani ab- 

 ftracled from their htuation and magnified ; a a the men^- 

 bi-ane ; b the flat head or dilk of the oiTiculum ; c the pedi- 

 cle ; d the extremity which unites with the cartilages, and 

 forms the triangle that is connecled to the membrana tym- 

 pani. Fig. II. exhibits a magnified view of a difleciion of 

 the labyrinth of the goof, in which the membranous parts 

 and the diftribution of the nerves are difplayed ; a the trunk 

 of the auditory nerve ; b the portio dura; ccc the three 

 branches of the portio molHs going to the femicircular ca- 

 nals ; d the nerve of the cochlea running in the fulcus, and 

 ram.ifying on the apex of the cartilages ; e the olfeous part 

 of the tube analogous to the cochlea ; /the inferior cartilagi- 

 nous cyhnder ; g the fulcus between it and the fuperior, 

 which is concealed from view by the nei-ve ; h h h the three 

 ampuUje of the membranous femicircular canals ; / thf cana- 

 lis major ; k tlie canalis minor ; / its communication with tl;e 

 major ; m the canalis minimus ; n the hole which corrcfponds 

 to the foramen ovale. Fig. 12. is the cartilaginous body 

 removed from the offeous tube ; a the fuperior cylinder ; b 

 the inferior; c their junciion where they commence ; d the 

 cavity at the apex of tiie cyhnder* laid open ; e the nerve of. 

 the cochlea ; /'its cxpanlion in the cavity of the apex of the 

 cartilaginous body. 



Organ of Sight. 



The pecuharities in the ftrufture of the eyes of birds are 

 chiefly intended to facihtate the perception of objects through 

 a rare medium, and accommodate vifion to different di- 

 ilances. 



Tlie/o/vn of the eye is admirably adapted in mod fpecies to 

 promote both thefe'effcfts. The anterior circle of the globe 

 of the eye always projects more than in other animals ; 

 and in many fpecies it is prolonged in a tubular form, and 

 in thofe cafes the cornea alfo is remarkably gibbous. The 

 oivl furniihes the moll flriking example of the difproportion 

 between Uie anterior and poflerior fpheres of the eye. The 



