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per ; he dlfcovered the communications between the cavities 

 of the bones and llie air-Cvlls of the foft parts, and afct-r- 

 tailed in a great number of fpccics what bones were tilled 

 with air. 



The refult of both his obfcrvations and our own tendu to 

 (liew, that the bones of birds are fupphed with air, accord- 

 ing as thty are employed in the locomotion of the ammal's 

 body. In birds of flight, therefore, almoll all the bones are 

 JioUow, and receive air ; thus in the englt Camper found the 

 air-cells communicatfd with the thigh bones, tliofe of the 

 pelvis and coxyx, all the vertebras, the (lernum, clavicles, 

 icapulae, and fork-lhaptd bone, and the bones of the wing. 

 The air was alfo admitted into the bones of the head from 

 the cavity of the tympanum. We have obferved the bones 

 in the hnwL iwAJIorilo want marrow in the fame manner as 

 thofe of the eaglt. Moll of the bones are hollow in the 

 Dzul ; but the os ftmoris is filled with marrow. T\ik f>i^con 

 Icind in general alfo have no air in their thigh bones, al- 

 though the crotvn p'l^eon has been obferved by Camper to 

 pofTcfs it. 



IMrds even of moderate powers of flight, receive fome 

 air into the fternum and other bones of the trunk, and be- 

 tween the platc« of their cranium ; and all birds, whofe wings 

 are not incapable of flight, have the humcius tilled with air, 

 with the exception of the -.coodcori, which has been obferved 

 to poffefs marrow in the humerus ; but to counterbalance 

 this impediment to the velocity of its motion, it is provided 

 with pefloial mulcks dF unufiial ilrength. 



Thofe birds which are unable to tranfport themfelves for 

 any diilance by the effort ot their wings, are deprived of air 

 in the humerus ; of tliefe may be inftanced all the Jlrutiiovs 

 kind, ihc fietit;iitn, the /''/^;;, &c. It is worthy of remark, 

 however, that ihc^flruthious birds, which run with great ra- 

 pidity, have moll of their other bones hollow ; Camper difco- 

 vered the air to pafs into the thigh bones and lower jaw of 

 the njlrich, and we have obferved that it fills not only thefe 

 bones, but the (lernum, the ribs, the vertebrx,and the bones 

 of the pelvis, in both the common ojlr'uh and that from New 

 Holland. 



The internal furface of thofe bones which contain air have 

 been dcfcribed by Camper as being in fome cafes lined with 

 periolleum, and in others entirely deprived of it ; thus he 

 ftates the internal part of the femur of the eagle to be can- 

 cellated and furnidicd with a periolleum, upon which feveral 

 blood-vefTels are ramified, and the humerus of the fame bird 

 to be a Cmple ofilous tube, without memb'ane, velfcls, or 

 cancelli. It appears to ur, however, that the membranes of 

 which the air-cells are compofcd, are continued in every iu- 

 Aance into the interior of the bone, to which they may ferve, 

 it is true, the purpofe of a periolleum, although in llruc- 

 turc they are much more fine and delicate, and when tiR-fc 

 membranes ceafe to be vafcular, they become dry, and adhere 

 fo clofely to the furface ot the bone, that they are not eafily 

 perceived. 



The internal parts of the bones of birds which are filled 

 with air confift of cells, like thofe of other animals; the 

 only didexence that can be obferved is, that the cancellated 

 iruAure is lefs clofc, and that the tube of the cylindrical 

 bodies, fuch as the humerus and femur, is larger than 

 ufual. 



It has been alr.eady mentioned, that the bones derive their 

 air in general trom tliofe cells which are placed next them 

 amongfl the mufcles. Some, however, a e filled immediately 

 from the lungs, or the large internal air-cells, and the hones 

 of the head and ja.vs have communications with the Eutla- 

 chian tube, tlie cavity of the tympanum, and the linufes of the 

 /lofe. 2 



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The huir.ei-us is fupplicd with air by the axillary cell, by 

 means of an opening fituated at the inner and back part of 

 the head of the bone. See /"/.;/? VI. in the Anatumy of 

 Birds ; fg, I. rtprefents the fupcrior half of the humerus of 

 the Amn-kan turkiy [jncl.cgns) ; <r the air hole, whicli like 

 the air-holes of the lungs, does not open imnitdiatcly uito the 

 cavity of the bone, but contains a number of fmallcr fora- 

 mina, that .'.re produced by the canctUi, and have a diredl 

 comvumication with the internal part of the humtniF. 



The fork-fliaped bone is hlled from the jugular air-cell, 

 from which alfo the fupcrior doilal, and the lowell cervical 

 vei tebra-, receive fome air, through feveral fmall holes Icat- 

 tered upon their lateral and anterior parts. The air-hole ot 

 the fork is placed upon the fide of its ieapnlar extremity, 

 next the fpinc. See Plate VI. in the Anatomy of Birdj ; 

 /'^•2. is the ore half of the tork-fluiptd bone of l\\c Jluri 

 viewed upon the infide, a the air-hole. 



The clavicle appears to obtain its chief fupply of air from 

 the cells which are continued from the jugular au-cells 

 backwards upon the {lioulder joint. 



The principal foramen is found on the infide of the 

 clavicle, where that bone is connetled to the branch of 

 the fork. There are btfides this, iome very minute holes 

 upon the outfide of the clavicle, immediately above the 

 (lioulder joint ; and on each fide of the Hernal extremity of 

 the bone, there is a hole large enough to admit a briftle. 

 See PlafeVl, in the Anatomy of Bhds. Fig. 3. fliewsau 

 internal view of the clavicle of X.\\t Jlurk ; a, the larger air 

 hole at the joint of the (houldtr; /, one of the fniall fora- 

 mina whicii opens into the cheft, containing a bridle. 



The fcapula derives air alfo from the procefs of the jugu- 

 lar Cell behind the joint. It is tranfmlttcd through feveral 

 holes upon the very extremity of the bone. See_/^. 4, of 

 Plate W. of the Anr.lomy of B'irdi, a the air holes. 



We have dilcovered the openings by which the air is con- 

 veyed into the (lernum, to be exceedingly nunitrous. The 

 principal foramina are firuated all along the middle line of 

 the bone, upon the internal turtace, w'hich appeal s reticu- 

 lated, or made of cancelli. Towards the anterior part there 

 is one hole much larger than any of the rell ; and in ad- 

 dition to thofe of the middle of the bone, there are many- 

 others palling into the edges of the ilernum to which the 

 ribs are articulated. All thefe foramina would appear to 

 communicate with the thoracic cells. See Plate VI. in the 

 Anatomy of Birds ; Jig. J. exhibits the internal furface of 

 the Ilernum of iXxsJiork; aaa the fmall foramina in the 

 middle of the bone, b the principal air-hole near the top of 

 the (lernum, c c c c many little foramina feen between 

 the ficrnal ribs which lead to the lateial parts of the 

 bone. 



The vertebrae of the back feem to procure air immediately 

 frc-.n the lungs ; the foramina are numerous, and placed 

 along the (ides of the bodies of the vertebrae and at the 

 roots of their tranfverfe procefles. Tiie foramina whicli 

 condndl the air into the cervical vertebiiE, occur with 

 as little regularity ; the three ilrit have their largefl 

 holes upon the lidcs of their bodies, and in the reft they 

 are to be found within the canal of the tranfverfe pro- 

 cefs for lodging the vertebral artery, and along the courfe of 

 the fpinal canal, at lead fo they have appeared in x\\cJ}ork. 

 See Plate VI. in tlie Anatomy of Birds. Fig. 6. flicws one 

 of the cervical vertebrre of that bird, a the body of the bone, 

 h the fpinous procefs, c c the tranfverfe pnicelTes forming a 

 portion of the vertebral canal, on the inildc of which are per- 

 ceived feveral foramina leading into the fubltauce of the bone, 

 i/the tube behind the body ot the vertebra for containing the 

 fpinal marrow, exhibiting many fmall holes upon its inter- 

 nal 



