B I R 



B I R 



The lalirdl thoracic cdh arc amongft the larjreft of the 

 body. They are of a pyramidal figure, their bafis being 

 applied to the intermediate thoracic cells, and their point 

 reaching as far down as the bones of the pelvis ; they cover 

 the inferior portion of the lungs, and occupy a fpace between 

 the ribs and the lobes of the liver. They have a very free 

 communication with the branches of the bronchise, at the ex- 

 ternal edge of the lungs. 



As the intermediate thoracic cells are fmall on the left, 

 and large on the right fiJe, thcfe cells are larger on the left 

 fiJe than on the right : this diiproportion is moft obfervable 

 in i\\i goofe, and very trifling in the ciuct, in which the two 

 intermediate thoracic cells are nearly of an equal niap;nitude. 



The air-cel!'5. which are found in the lower or abdominal 

 portion of the c.ivity of birds, are compofed of thinner mem- 

 branes than the others ; in fome parts they are fo tender, 

 th'it they are ruptured with the fligiitell: touch, from which 

 they beco'iie very difficult to examine. 



Underneath th;- lateral thoracic cells, at thf veiy loweft 

 part of the lungs, on each lide of the fpine, the branches of 

 the bronehiae open into the cavity of the abdomen, by which 

 means air is conveyed dn-ri^ly mto the tv.-o great lateral ah- 

 dominal cells, and from thefe it would appear tliat it pafTes 

 into the others. 



The Literal Gbdonv.nal cell of the riglit fi 'e is by much the 

 largf-(l in the body ; it reaches from the laft ribs to the anus, 

 and lies over and includes almoft all the fmall inteftines, the 

 renal capfule, and the kidney. It appears in the goofe to be 

 divided from the oppolite cell by a membrane which pafles 

 obliquely from the right fide of the anus to the lower part of 

 the gizzard. 



The left lateral abdominal cell contains the inteftines of 

 that fide ; it is attached to the margin of the gizzard, under 

 which it is prolonged as far as the lungs, where it is fupplied 

 with air, as already mentioned. 



The lateral abdominal cells tranfmit air to the inguinal 

 cells, and to feveral chambers formed by the moll delicate 

 membrane, amongft the inteftines. One of thefe being 

 fomewhat ftronger than the others, there was an opportu- 

 nity of obferving it more diftinftly. It maizes a circuit 

 around the right fide of the gizzard to which it is attached, 

 and inclofes the duodenum and pancreas ; it might thence 

 receive the name of the duodenal cell. 



Interpofed between the parietes of the belly and the la- 

 teral cells there is frequently found a confiderable quantity 

 of tender fat ; efpecially in aquatic birds, fuch as the goofe, 

 &C. By this means a foft cufhion is provided for the fmall 

 inteftines to prefs and move upon, thus fupplying the ufe of 

 the omentum, which is a part not met with in birds. 



The ftrufture of the air-cells of birds in general does not 

 appear to be the fame dcfcribed in the ojlrlch and caffbtuary 

 by the academicians. The membranes compofing them iu- 

 ilead of being diftinft bags, as they relate, refemble rather 

 the pleura or the peritoneum, and like them, feem to pro- 

 duce all the different cavities by the means of reflection. It 

 muft be confeiTed, however, that the membranes of the cells, 

 efpecially in the abdomen, are very eafily f.'parable into dif- 

 ferent lamina, or layers, which, it might be fuppofed, could 

 be ultimately refolved into diftinft facks. 



It deferves to be mentioned, that each of the air-holes in 

 the furface of the lungs opens obliquely into the air-cells ; 

 there being a flight projeftion of thin membrane over tlie 

 aperture. The Parifian anatomifts afcribed a valvular effect 

 to this llrufture, which they fuppofed of great confcqnence, 

 as it would ferve to continue the didenfion of the air-bags, 

 after they were once inflated. The projection of the mem- 



brane over the air-holes does not however appear to be fnfH- 

 cicnt to caufe any oliflruAion to the regrefs of the air from 

 the cells ; nor would it feem necelfary or convenient to in- 

 terrupt in the Icatt degree the expulfion of the air contained 

 in the ells. 



The membranes of which the air-cells are compofed, are 

 refledted into the apertures of the air-holes, and are there 

 perforated by a great number of fmall foramina, which cor- 

 refpond to the termination of the ramification of the bron- 

 c'ii3e, through which the air has a ready pafTage. When 

 thefe foramina are brought into view, by diffefting of the 

 coverings ot the lungs, they give the anterior furface an ap- 

 pearance of being pricked by pins. 



The air-cells which are found amongft the mufcles and 

 integuments of the external parts of the body, vary in 

 number and magnitude, according to the ftrudure and 

 economy of the bird. In every inltance, perhaps, the an- 

 terior thoracic or jugular cell is continued along with the 

 vcflcls and nerves into the axilla, making what may be 

 called an axillary cell, and in moft birds others go off from 

 this anteriorly under the peroral mufcle, and backwards 

 under the mufcles of the fcapula, fornnng/if-iS'srrt/ and _/ai- 

 fcapular cells. In the eagle, ha'wh,Jlorh, lark, and other high 

 fiying birds, thefe cells are very large, and in many of thofe 

 birds there ai-e itill larger cells, afcending under the integu- 

 ments of the neck, and paffing beneath the fliin of the in- 

 fide of the arm, and the back of the (houlder. In \.\\e fork 

 we foU':d thcfe cells large enough to admit the finger to 

 pafs a confiderable way dcfwn upon the infide and the back 

 of the wing. They are alfo large in the owl and other 

 birds of pi-ev. 



Moft birds of flight have a number of cells placed under 

 the lateral mufcles of the neck. Thefe are oppofite to tlie 

 bodies of the cervical vertebrae, and communicate with one 

 another. It is from the diflerent cells about the axilla and 

 neck, that the bones of the fhoulder, the humerus, and the 

 vertebra:, receive the air which they contain. 



The Inguinal and gluteal cells are filled from the great 

 lateral cells of the abdomen, with which they have a com- 

 munication, where the blood vcffels of the lower extremities 

 pafs out of the pelvis. The inguinal and gluteal cells fur- 

 round the neck of the femur ; they are in moil birds very 

 fmall, but in thofe which are much employed in flighty 

 efpecially if the thigh bones receive air, they arc larger, 

 extending for fome way amongft the mufcles behind the 

 joint. Camper obferved two air bags between the glutaei 

 mufcles of the gemn f/>oo/dlll (//d.'a/ira), although no air was 

 tranfmitted into the femur. 



The fubcutaneous air-cells of the pelican are very large, 

 and were dcfcribed long ago by Mery,in the early Memoirs 

 of the Academy of Sciences of Paris. 



Several means have been employed to prove that the air 

 is permitted to enter the cavity of the bones in birds. The 

 air-cells and the lungs have been inflated from the bones, 

 and injedion being thrown into the trachea, was found, 

 after diftending the air-cells, to have palled into the interior 

 of the bones. A ftill more dccifive experiment (although a 

 cruel one) is to cut the humerus acrofs in a living bird, and 

 introduce the extremity of the divided bone into water, in 

 which fome foap has bc-n diffolved, when it is perceived 

 that bubbles are produced by the exit of the air from the 

 end of the bone. This expedient not only afcertains the 

 exiftence of air in the bone, but fbtws that there is a mo- 

 tion or circulation of it, which is the effect of the adions of 

 infpiration and expiration. 



This fubjcfthiis been very extcnfively inveftigattdby Cam- 



