4 SURVEYS OF NATURE. 



for the motion of their wings, and becaufe the body of air does 

 not he fo dired:ly under the wing as they rife. 



The office of the peroral mufcles being to move the wings, 

 they are endowed with pecuhar ftrength: the ftroke ofafwan's 

 wing would break a man*s leg, and fiich a blow from an eagle has 

 deprived a man of life. Befide mere flrength, they have occafion 

 alfo for perleverance: their efforts rnufl: often be maintained long 

 together; and this in birds of paliage is remarkable: they poffels 

 not the power of an eagle, but poliibly they exceed many of that 

 kind in continuance; fome birds feera always flying, and are found 

 hundreds of leagues from fl^ore, ever on the wing. 



The toes in fome are webbed, to fit them for the waters; in 

 others feparate for their better clafping. Thofe with long lega 

 have alfo long necks, or how could they gather their food ? But 

 thofe with long necks have not always long legs; we inftancQ 

 in fwans and geefe. 



The bones of birds are extremely light and thin though com-« 

 pa6t, and the mufcles (except thole moving the wings) extreme-? 

 ly flight. The tall, which is compofed of quill-feathers, 

 balances the head and neck ; direds their flight like a rudder, and 

 greatly aflifts in defcending. 



We find by ourfelves, that rapid motion fpeedily induces dif-r 

 Acuity of breathing; yet the principal mufcles ufed in fuch exer-f 

 cife, are not feared around the lungs: were our arms exerted with 

 equal violence (of which they are unable) their effe^s might be 

 greater. To prevent this impeded refpiration in birds, their lungs 

 (commonly called the fole) adhere to the ribs and back, and very 

 little dilate or contrad*. But the branches of the wind-pipe 

 open into them, while thefe open into the cavity of the belly, and 

 convey the air inhaled by breathing into certain receptacles like 

 bladders, running the length of the whole body: lo that air 

 blown into the wind-pipe will difl:end the animal's body like a 

 bladder ; confequcntly they have great facility of long and large 

 infpiration. Sometimes alfo the wind-pipe makes many convolu-* 

 tions within the body of the bird, and is then called the laby- 

 rinth; but of what ufe are thefe convolutions is not known, 



I fufpea 



