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which is often pmlonjred for fome way betwfen the lobes of 

 the liver. It dtfcrvtfs remark, that notwithftaiidiiig the 

 gfL-at lize of the pcrioardium, the air, which pcrvadc-5 almoll 

 all the cavities of birds, i'i not admitted into this. The Pa- 

 rifian academicians, it is true, obferved the pciicardiiim to 

 fivell wlicn they inflilcd the lim;'s and air-cells of ihe ptnta- 

 i!o, and tliencc conchided that the air had admilTun to the 

 licart, for which they a(ris;ned fome curious reafons ; inch as 

 the heart req^irinp comprt-nTiou and evaporation from its 

 furface. They appear, however, to have been equally in 

 error with rcfpeit to the faft and the reafoninp ; tor, in a 

 great number of fpecics we have examined for the purpofc, 

 the pericardium was uniformly found to contain a certani 

 quantity of water, and !iad not the lead communication with 

 cithtr the lungs or air-ccl!s. The Parifian anatomifts mull 

 have been led into this miilake by the dillenlion of the air- 

 cells around the pericardium. 



The heart is of a longer fi Turc in birds than in other ani- 

 mals ; and the outline of the right iide is flightly concave, 

 in confequence of the parietts of the right ventricle being 

 relatively thin. In the ojlrtch, the heatt has been defcribcd 

 as nearly round ; mcafuring fix inches from the bafe to the 

 apex, and live inches acrols. 



Birds have, like mammalia, four dillinfl cavities in the 

 heart, which bear the ul'ual proportions in magnitude with 

 refpeA to each other. The auricles however, and efpecially 

 the right, are commonly more mufcular than in other ani- 

 mals ; and the left ventricle is always much Itrongcr than the 

 light. 



The internal furface of the auricles is very irregular, in 

 confequence of the Ihape and fixe of the mufcular falc.culi. 

 There is one very ilrong portion of mulcle, which enters in- 

 to the compofition of the auricular pat of both cavities, 

 from which other fafciculi proceed in a regular and radiated 

 manner, at Icall m the right auricle. See Plate V. in the 

 Anatomy of lii/ds. Fig. 3. Ihews the heart of the goofe, with 

 the auricle and ventricle of the right fide laid open, e the 

 principal mufcular lafciculus of the auricular portion of the 

 cavity pafung b:ickwards towards the left auricle ; _/ the lef- 

 fer fafcicul', which depart from the other as branches from a 

 trunk ; gg the deep foffa; which exill on each fide ol the 

 large fafciculus. 



The blood of the vifcera and lower limbci is conveyed into 

 the riglit auricle by a vein correfponding to the inferior vena 

 cava of mammalia. There is, however, no vein llriilly ana- 

 logous to the fuperior cava, the veins of the right wing and 

 that fide of the head and neck, forma diilinft trunk, which 

 enters the upper part of the auricle ; while thofe of the op- 

 polite fide alfo produce another trunk, which paffes along 

 the poftcrior furface of the left auricle, to which it is elofcly 

 united, and opeiu into tlie right auricle belide the inferior 

 cava. 



The anatomifts of the French academy obferved, in moft 

 of the birds they dilfefled, a valvular projection of the inner 

 membrane of the heart, over the entrance of the inferior 

 vena cava into the right auricle. This valve refembles in 

 form that of the coronary vein of the human heart, and by 

 its means, the orifice of the cava, which is really very large, 

 puts on the appearance of a narrow flit. A fimiliir valve 

 hangs over the entrance of the veins which return the blood 

 of the wings and head to the auricle. See Plate V. in the 

 Anatomy of Birds, fig. ■*!. aaa point out the veins, which 

 terminate in the right auricle with their valviJar orifices, into 

 «ach of which a brillle has been introduced. 



The analogy between the valves of the veins entering the 

 right atiricle of birds, and the Eullachian valve of the human 



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heart, is very obvious, and demonllrates, as far as analogon* 

 llrudure can, that the latter fervcs the purpofe of a valve to 

 the vena cava in the human fiibjed. 



There are commonlv two or tiirce orifices for the coro. 

 nary veins in birds, one is always larger than the reil, and 

 tranfmits the blood of the principal vein of the heart. They 

 are each provided with a (light projection of the inner mem. 

 brane, which afts iinpcrfedlly as a valve. 



The right ventricle is of a triangular figure, and is quite 

 fmooth on the internal furface ; there being none of thofs 

 procefles of mufcle which are called carncir coliminnc. 



The valve, which is p'aced at the mouth of therig'it ven- 

 tricle, is of a peculiar fliape and llruClure in birds. Iiidcad 

 of thofe thin and membranous folds, which ufually fiirround 

 the orifice of the ventricle, and are moved by iiitana of 

 their connexion with the carneas coliimnse, and which from 

 their figure in the human fubjedt are called the Irkufpid 

 valve ; there is a fingle projection of the flefii of the heart, 

 of a triangular figure, and nearly as thick as the parities of 

 the cavity in which it is contained. The triangular valve is 

 joined by its fuperior edge to the margin of the orifice of the 

 ventricL', and is united by another of its edges to the right 

 fide of the cavity almoil to the bottom. The third edge is 

 uncouneftcd, except bv a finall procefs, wliich goes off near 

 one of the fuperior angles to the parietes of the ventricle on 

 the left fide. See Plate V. in the /Inatomy of Bu-ils, fig. 3. 

 b the triangular valve, expofed by means of the anterior pa- 

 rietes of the right ventricle being cut off, a briltle is palled 

 under the valve ironi the auricle } ilddihe external furface 

 of the heart ; c the procefi connecting the floating edge of 

 the valve to the parietes of the ventricle, with a brillle lying' 

 under it. 



The triangular valve, from its thieknefs and mufcularity, 

 would feem to operate chiefly by means of the contra£tion 

 of its own fibres changing its figure, and thus obltru(Slin£r 

 the return of the blood into the auricle. Borrlchius difcovercd 

 a foramen in the feptum of the heart of ihti pig:oii, large 

 enough to admit a brittle, by which the two ventricles had a 

 direct communication with each other. S^e Aft. Dan. anni I, 

 oblerv. 96. ; and we have obferved tlie fame foramen at 

 tlie upper part of the feptum of the heart of the goofe in one 

 inllance ; it was of fuffieient fize to receive a crow quill. 

 Such a communication does not appear, however, to be an 

 uniform or natural llrufture, as we failed to difcover it in 

 other geefe, and in diiTerent fpecies of birds examined for the 

 purpofe. Indeed, a ready communication betwe<n the ven- 

 tricles of an adult bird, would be inconfiftent with the mode 

 in which the functions of refpiratioa and circulation are car- 

 ried on in this clafs of animals. 



The pulmonary artery is provided with three femicircular 

 valves, as in mammalia. It divides alfo, as uliial, into a vef- 

 fcl for each lung, and that of the right fide palTes under the 

 arch of the defcending aorta. 



The blood is returned from the lungs by two pulmonary- 

 veins, which open very near each other into the upper and 

 pofterior part of the left auricle. 



The mechanifin of the cavities of the left fide of the heart 

 more nearly refembles that which exifts in mammalia. The 

 films, or membranous part of the left auricle, is however very 

 Imall, and of an oblong (hape ; and at the place where the 

 pulmonary veins enter into the auricle, there appears to be a 

 projection ofthe internal membrane, which performs the office 

 of a valve to their orifices. 



The valve of the left ventricle is thin and membranous, 

 and refembles fo much the mitral valve of the human heart, 

 that the fame name might with propriety be givea to it. 



The 



