38G 



RESPIRATION OF BIRDS. 



the venous blood coming in contact with the oxygen, when 

 passing through the capillary vessels of the general system, as 

 well as when it passes through the pulmonary capillaries. The 

 lungs are not divided into lobes as in the Mammalia, and are far 

 from filling the thorax ; they adhere to the ribs ; and they 

 present at their inferior surface many openings, belonging to the 

 bronchial tubes, which traverse them in different directions, and 

 carry the air into the air-cells distributed among the different 

 organs of the animal. These cavities are formed by membranous 

 partitions, or by lamina? of cellular tissue, and communicate with 

 one another ; some are found in 

 the trunk, of very considerable 

 siz" ; and others are prolonged 

 towards the head, and between 

 the muscles of the limbs ; the air 

 thus finds its way into every part 

 of the body, and generally also 

 into the substance of the bones. 

 An examination oi the air-cells 

 in different Birds, shows that the 

 quantity of air thus distributed 

 into the different parts of the 

 body, varies, other tilings being 

 equal, in proportion to the energy 

 md continuity of the movement- 

 of the animal ; thus in Eagles, 

 Sparrowha-Ak-, and other Birds of d.tht- trachea; ,-. tlu-li 



powerful flight, this fluid pen.'- tli.^o ;\ir -c-lls fimm 



trates into all th" !><>:ie- ; \vlnlc lun R s - 



in tho-e which are destitute of the power of flight, and which 

 IVn.i'.in-. \c., it is excluded from the 

 from the whole of the skeleton. The air 

 rreatest abundance in the bones of the limbs 



walk but slowly, a- 

 '_avater part, or even 



most employed in locomotion; thus in the Ostrich, the femur 



(thigh-bone) present- a remarkable development of the air-cells. 



!J4 ( J. Birds have :( more constantly-active respiration than 



any other animals; they consume more oxygen in proportion, 



