B I R 



It mlqht be ofTi-red in objeftion to tliis opinion of the ufe 

 of tht air-c<rlls in birds, that the bat, whicli is an animal very 

 rcirarkaSV- for the velocity of its flight, and its long conti- 

 nuance on the wing, is unfurnifhcd with any apparatus except 

 its lungs for containing air. The anfwcr to this, howcve--, 

 is ver)'cafv; the exrtnt of th- wing of the lat is fingiilarly 

 large for the animal, and its membranous llrudine enables it 

 to give impuH'e to a larger vohime of air than could be pro- 

 ducid by a wing compofed of feathers, even ot an equal ex- 

 tent ; and fu-'thrr, the p ftoral mufcles of the bat are larger in 

 proportion to the animal than they are found in any fpccits 

 of birds, even tliof.- of the higlicft flu'ht ; fo that the ilrnc- 

 tureof the lat, iiillead of proving any ohjeaion to the ufes 

 affigned to the air-cells in birds, aifords the llrongea conlirm- 

 ation of the theory. 



Notwitlillanding the refpca which is due to ever^' phy- 

 fiologicai opini .n of Mr. Huntu", wc cannot perceive that 

 there i» the leall relation between the air-cells and the 

 organs of voice in birds. With a view of determining this, 

 wc have compared the ilrudure of diflcrent birds, and have 

 not found the air-cells larger in fmging birds, than others. 

 The nishlin^alf, fo eminent for its loud and protraded notes, 

 is formed, with refpcd to the air^ells, exaftly like the 

 common fparroiu. 



Animal Heat. 

 Although it is not yet proved that the vital temperature 

 of animals is the refult of that proceis which is called rel'- 

 piration ; yet, as it is generally fuppoled to be fo, it would 

 appear moll proper to notice the animal heat of birds, im- 

 mediately after the dcfcriptioii of the lunirs and their ap- 

 pendages. It is rcinarkablt, that birds pofl'eis a hitjher 

 ftandard of vital temperature than all other animals. Cam- 

 per ft.uc» it to vary from IC4 to 107 degrees ot Fahren- 

 heit's fcale. Mr. Hunter found the redum of the common 

 fowl to be IC3, 103}, and 10+ degrees; and in a young 

 goofe, we obfervcd the thermometer to Hand at 103 degrees 

 in the reflum, ard whtn infcrted into the cavity of the 

 body, to rife and remain at 1:4 degrees. It is difficult 

 to explain either the caufc or the ncceffity of the high tem- 

 perature of birds. It has been accounted for by their rcf- 

 pi-ation being more perfed from the air paffing twice 

 through their lungs ; but even fuppofing this would a'tr 

 their degree of animal heat, the occafion docs not feeni to 

 exift, as birds have not that double rcfpiratioii which is 

 fuppoftd, as has been already (hewn. 



It is to be prefumcd, that the warmth of birds may de- 

 pend, in a degree, upon the llrufture of their fkin, and the 

 nature of their coverings, which are not delignrd to admit 

 of much evaporation from the furface of their bodies ; bi:t 

 it can hardly be fuppofcd, that this, of itfclf, would be 

 fufficient to produce a temperature fo much higher than is 

 found in other animal?, and maintain it '"o uniformly and 

 permanently as it exifts throughout the whole clafs of 

 birds. 



No experiments have yet been made to determine the 

 powers which birds poffrfs of refilling the influence of ex- 

 ternal temperature ; but it is to be inferred iVom analogy, 

 that they can fullain greater extrem.ts of both heat and cold 

 than ether animals, without fuffering an alteration in their 

 proper degree of temperatuie ; but that, at the fame time, 

 birds would fooneft yield to diffoiution upon any material 

 cha 'ge in their natural ftandard, it being found that ani- 

 mals generally enjoy independence of tempcratuie, in pro- 

 portion as it exceeds that to which they are commonly ex- 

 pofcd, and that the higher their natural ftandard, the more 

 inconvenience arifes from any alteration of it. 



B I R 



Blood Ve[[ch. 

 The organs of circulation in birds have obtained but lit 

 tie of the attention of comparative anatomifts. The larger 

 branches of the arteries and veins, which lie near fome o£ 

 the vifcera, have alone received any defcriptiou ; and that 

 rather from being involved in the account of other parts, 

 than for their own fake. The diftribution of the blood 

 vclfels of birds, notwithftandiiig this, is not the Itaft intercfl- 

 ing part of their anatomy, as will appear from the enfuing 

 di-fcription, which has been taken chiefly from the fwan, 

 goofe, duch, Jlork, ?i\A common fo-wL in which it was found 

 fo much alike, that it may be prefumed the fanae arrange- 

 ment of the blood vtd'els prevails with little variety in all 

 birds. 



The /Irteries 

 Proceed from a fingle trunk which arifes from the left 

 ventricle of the heart. This trunk is fo (liort, that it is 

 concealed by tlic other parts on the bafis of the heart, and 

 is only brought into view after the reflexions of the peri« 

 caidium, and the adjoining veffcls are detached by diflec- 

 tion. It is from thence, that as the parts are commonly 

 beheld, there appear to be three great arteries ifTiing toge- 

 ther from the middle of the heart, which are tiie primary 

 branches into which the aorta is divided. The firft branch 

 is to the left fide, and after it is fent ofi^, the trunk affefts 

 to turn over the auricle, before it gives the branch of the 

 right fide ; thefe two branches pafs in a curved manner 

 from the heart towards the axills, in the form of horns, 

 and each is analogous to xhtariiria Innom'mata of the human 

 fubjeft, fo that iiiftcad of one, there may be reckoned two 

 arteritr innommals in birds. After thefe branches are parttd 

 with, the arterial trunk is continued over the auricles, and 

 on reaching the back part ot the heart, becomes the dejcend- 

 ing ao' la. 



The nrteria imiominata firfl fends off" the common trunk of 

 the carotid and vertebral arteries, which before its divifion 

 gives off one or two fmall branches ; one of thefe runs down 

 upon the lurgs in company with the pa- vagum, and appears 

 to fupply branches to the aponeurofis of the lungs, and the 

 air-cells at the upper part of the thorax ; the other branch, 

 after fupplying the lymphatic gland of the neckn\ith fcveral 

 fmall arteries, afcends upon the fide of the afopTiagi's, to 

 ivh'ch. and the in'eiior larynx, the divifions of the trach'ra, 

 and to the parts and Miteguments of the fide of the reck, its 

 branches are dillributed, a'lallomofing with the fuperior 

 osfophageal and tracheal arteries. This branch is often not 

 f.-iit ofl until the trunk divides into the vertebral and carotid, 

 in which cafe it comes from the latter artery. Sometimes 

 in the duck, the fvpra-fcapular artery, which is ulually 

 derived from the vcitebral, is a branch ol the common 

 trunk 



The carotid artery, after parting from the vertebral, pro- 

 ceeds to the middle of the neck, and foon difappears ; being 

 covered by the mufcles of the anteri.r p.^it of the neck, 

 under which it lies hidden, and in clofe contact with its fel- 

 low of the other fide, to very near the head. If, during its 

 courfe in this fituation, it gives any branches, they are too 

 infignificant to be noticed. 



The carotid artery emerges from between the mufcles of 

 the neck, at about the third or fourth vertebra from the 

 bead ; and after giving a branch downwards, amongft the 

 lateral mufcles of the neck, it runs along the outer edge 

 of the reftus major anticus mufcle, to behind the angle 

 of the jaw, where it divides into its feveral branches. 



An artery firll goes off polleriorly, which pafTes a little 

 forwards under the branch of the os hyoides, and after fend. 



ing 



