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into tliree kinds, i. Thofe of the grezt cavity of their 

 body which takes the place of the thorax and nbdomen, 

 2. Thofe fituatcd amongft the mufcles ; and lallly, thofe in 

 the interior of their bones. 



It lias been already dated, that the body of birds is not 

 divided into two parts by a tianfvcrfe mufcular partition or 

 diaphragm. Tliis common cavity is intcrfcAcd by a great 

 number of membranes, fomc of which fnnply enclole 

 the fevcial vifcera, but the greater number form cells, 

 which arc filled from openings upon the furface of the 

 lungs. 



Thefe membranes are in moll birds extremely fine and 

 delicate, often fo much fo, that the vifcera are perfeflly 

 vifible through them ; they arc alnioft impoffible to be difTedl- 

 ed unlefj when kept continually iriflated, by blowing into the 

 trachea ; it is faid, however, that in the nfirich and cajawaiy, 

 they are as (Irong as a hog's bladder. 



The anatomifts of the academy defcribe the heart and 

 liver of the oflrich as contained in one cavity, which was 

 unfumiflied with air, and was fcparated from the air-cells 

 on the lide by two longitudinal membranes, and from the 

 lloinaoh and inteftines below, by a tranfverfe membiane, 

 fituatcd like the diaphragm of mammalia, and covered on 

 its inferior furface by a layer of fat, of the thicknefs of a 

 finger ; in all the birds, however, which we have examined, 

 vve have found a membrane inclofing the pericardium, in the 

 manner of the medialHnum, and afterwards reflefted upon 

 the liver, and then forming two fack<!, of which one con- 

 tained the right lobe of the liver, and the other included 

 the left lobe, along with the anterior furface of the gizzard ; 

 and in the goofi, and fome other birds, the membranous 

 fack of the left fide of the liver only admitted into it the 

 upper half of the anterior part of the gizzard ; in general, 

 no air is found in the cells which enclofe the liver and the 

 tmterior part of the gizzard ; wc, however, once inflated 

 them from the trachea in the gooje, in which they had a 

 communication with the cells of the abdomen, by means 

 of three large holes ; but it is probable, that this was from 

 mal-conformation of the membrane. 



The air cells of the great cavi'y of birds, according, to the 

 academicians, who take their defcription from the ojlr'ich and 

 the cajfotvary, are five on each fide of the body. The four 

 fuperior cells are immediately next the aponeurofis of the 

 lungs, and are fcparated from the reft of the cavity by a 

 ftrong membrane which defcends from the top of the thorax 

 upon each fide to be joined to the tranfverfe membrane which 

 divides the heart and liver from the llomach and inteftines. 

 The inferior cells are by much the largeft, and are kept 

 dilUnft from the inteftines by a ftrong membrane, fimilar to 

 the other partitions of the cavity, they come in contaft with 

 the aponeurofis of the lungs, only at their fuperior part, 

 where they receive their air. The uppermoft cell is the 

 fmalleft, and derives its air from an opening at the fuperior 

 part of the lungs. The next cell is of a fquare figure, and 

 is filled by means of two foramina fituated upon the exter- 

 nal edge of the lungs. The third cell of each fide is not a 

 regular fquare, being of greater extent where it joins the 

 lungs than at the oppofite fide ; it has but one communica- 

 tion witli the bronchia, which is placed upon the internal 

 margin of the lungs. The fourth cell is of a very irregular 

 elongated form, reaching down to the bones of the pelvis ; 

 it is lefs cxtenfive in the cajfonuary than in other birds. The 

 air-hole of this cell is fituated at the loweft part of the lungs. 

 The lull or inferior cells are long, and femewhat of an oval 

 ftiape ; they communicate with the moft inferior point of the 

 lungs. 



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The Parifian anatomifts defcribe all thefe cells an hem^ 

 formed of dilliiia tunics, fo that each is a fcparate bag, in- 

 Head of being made by continuous and rcfleded membranes. 

 They rtprefent the bags to be diftinCl alfo from the great 

 membranous partitions of the cavity. See PlaleV. in the 

 yiiiiifniiiy of Birds ; fig. 4. is copied from the memoirs of the 

 French academy, and exhibits the air cells, &c. of the 

 cjlrich ; a the trachea ; b b iht two bronchia; paffing to the 

 lungs; ("the heart; and (/rf the liver, feen in the fuperior 

 divifion of the cavity ; e the tranfverfe membrane which fepa- 

 rates, like the diaphragm, the common cavity into two parts ; 

 /the ftomach ; and ^_f 5- the convolutions of the inteftine, 

 feen in the lower or abdominal portion of the cavity ; h hhh 

 the lateral partitions which inclofe the four fuperior cells ; 

 12^45 indicate the dift"crent cells ; the air holes are appa- 

 rent' in each, except the inferior or abdominal cells, which 

 cannot be brought into view, as they lie behind the fourth 

 cells. 



The air-cells of birds in general do not exaftly accord 

 with the defcription given of the ojlnch and cajfcwciry, by 

 the members of the Royal Academy ; we (hall tlicrefore 

 proceed to give an account of what we have obfcrved on this 

 part of the anatomy of birds in the goofe^ duck, common fowl, 

 pigeon, Sic. ; and in order to make this defcription more in- 

 telligible, we fliall take the liberty of naming the cells ac- 

 cording to their fituation with refpeft to other parts, although 

 fome of the terms muft be adopted upon the ilrength of 

 analogy, as the diftinftions of thorax and abdomen do not 

 with ilriftnefs belong to birds. 



The firft is t\ic fuperior thoracic, or jugular air cell. When 

 it is diftendtd with air, it becomes evident upon the outfide 

 of the thorax, between the two branches of the fork ; it is 

 large enough in the goofe to contain an apple in its anterior 

 part, and pofteriorly it extends on each fide of the bafis of 

 the heart, over the lungs. This cell contains the divifions 

 of the trachea into the bronchice, and the trunks and pri- 

 mary branches of the blood-veffels which fupply the wings 

 and head. A great number of membranous ftpta pafs 

 through it in various direftions, which ferve to conneft and 

 keep fteady the different vefiels, and alfo divide this cell into 

 feveral chambers, which, however, have all a free communi- 



cation with each other. The air is tranfmitted from the 

 fuperior part of each lung by two openings which are placed 

 in the pofterior chambers of this cell. Thefe chambers do 

 not appear to extend fo far upon the lungs in other birds as 

 they do in the goofe ; it is from this cell that the air pafles 

 into the cells of the axilla, and under the fork-ihapcd bone, 

 into the deep feated cells of the neck, and to thofe about 

 the (houlder. 



The next cells may be called the intermediate thoracic. 

 They are generally two in number, one to each fide ; they 

 lie immediately upon the lungs, and are in a degree co/ered 

 by the anterior thoracic cell. That of the right fide is 

 ufually larger than the one on the left ; the latter is particu- 

 larly fmall in the goofe, being almoft concealed by the two 

 adjoining cells, and extending under the poltcrior part of the 

 liver. The cell of the right fide is of an oblong fquare 

 figure, and is prolonged under the termination of the inferior 

 vena cava in the right auricle, as far as the left fide of the 

 bulbus glandulofus. The intermediate thoracic cells receive 

 their air through a large foramen, fituated upon the inner edge 

 of each lung, juft at the bafis of the heart. At the upper 

 and inner angle of thefe cells alfo there is an opening which 

 appears to lead to fome fmall cells under the pericardium and 

 cefophagus, and to communicate indireftly with the anterior 

 thoracic celL 



The 



