74 8 



THE POPULAR SCIENCE MONTHLY 



-p 



proportionately the largest among animals. In some species the skin 

 is quite as active as the lungs, and the latter can be removed without 

 causing immediate death. 



The lungs of birds are less developed structurally than those of 

 mammals, but are much larger. Connected with them in various parts 

 of the body are air-sacs, especially in the abdomen and beneath the 

 skin of the neck and wings. Except in water-birds, the hollow 



bones also contain air, and 

 by their connection with the 

 lungs respiration can be con- 

 tinued through an opening in 

 the arm or thigh-bone, al- 

 though the windpipe may be 

 tied. 



The respiratory system is 

 ) most developed in birds of 

 n powerful flight, and doubtless 

 aids in rendering them buoy- 

 ant. Perhaps the air-sacs be- 

 neath the wings assist in hold- 

 ing the latter outstretched ; 

 and it has been suggested that 

 the sacs might serve as a cush- 

 ion to protect those which sud- 

 denly dive into water after 

 prey. 



The blood-capillaries in the 

 lungs of reptiles and amphib- 

 ians are exposed to the air on 

 one side only, while those of 

 birds and mammals are ar- 

 ranged on a different and su- 

 perior plan, being exposed on 

 two opposite sides. Lungs of 

 birds consist of an aggregation 



Fig. 9. General \ iew of the Air Reservoirs of . 



THE )>[CK, OPENED INTERIORLY; ALSO THEIR RELA- Of dlStlnCt lOOUleS 01* lllllg- 



tions with the principal Viscera of the Trunk. . . , . 



1,1, anterior extremity of the cervical reservoirs; lets. As the lungs are at- 

 2, thoracic reservoir; 3, anterior diaphragmatic -, ., n , _ n e 



reservoir; 4, posterior ditto; 5, abdominal reser- tachea to the dorsal Slue Or 



voir. , membrane forming the anterior diaphrag- .-, , i ., t- i 



malic reservoir; &, membrane forming the posfe- the chest, and the diaphragm 



rior ditto. 6, section of the thoraco-abdominal dia- n . .*. j? 



phragm. d, subpectoral prolongation of the thoracic 1S imperlect, expiration IS ei- 



reservoir ; e, pericardium; /'./; liver; a, gizzard; x* + /i l.,, ., +;,,^ ^flF^,.f l^r 



A. intestines: m, heart: , re, section of the great tected by an active eftoit by 



pectoral tnnscle above its insertion into the hume- nil ii; no . the hrp-mt-bonp nearer 



ru<; o, anterior clavicle; p, posterior clavicle of the P uuin g lUe oieasi uone maiei 



p i ey' t 8 8 wo 3 rk U ) tand """"^ oatward> (FromM.Sap- the gp i nej ana s0 diminishing 



the cavity. 

 While reptiles can live in air too impure for mammals, birds will 

 die in an atmosphere which to mammals is quite harmless. Birds bear 



