209 



CHAPTER XX, 



RESriKATORY SYSTEM OF BIRDS. 



§ 156. Lungs of Birds. Xotwithstanding the extent and ac- 

 tivity of the respiratory function in Birds, the organs subser- 

 vient thereto manifest more of the Reptilian than of the Mamma- 

 lian type of formation. 



The lungs are confined, as in the Tortoise, to the back part of 

 the thoracic-abdominal cavity, being firmly attached to the ribs 

 and their interspaces ; and, as in the Serpent, they communicate 

 with large membranous cells which extend into the abdomen and 

 serve as reservoirs of air. In the Apteryx alone they do not 

 penetrate the diaphragm. 



In those aquatic Birds which are deprived of the power of 

 flight, as the Penguin, the air-receptacles are confined to the 

 abdomen ; but in the rest of the class they extend along the sides 

 of the neck, and, escaping at the chest and pelvis, accompany 

 the muscles of the extremities. They also 

 penetrate the medullary cavities and diploe 

 of the bones, extending in different species 

 through different proportions of the osseous 

 system, until in Volitores, even in the Horn- 

 bill, every bone of the skeleton is per- 

 meated by air. There is, indeed, no class of 

 Animals so thoroughly penetrated by the 

 medium in which they live and move as that 

 of Birds. 



The lungs are two in number, of a length- 

 ened, flattened, oval shape, fig. 95, extend- 

 ing along each side of the spine from the 

 second dorsal vertebra to the kidneys, and 

 laterally to the junction of the vertebral with 

 the sternal ribs. They are not suspended 

 freely, nor divided into lobes, as in Mammals ; 

 but are confined to the back part of the chest by cellular 



VOL. II. p 



Kiglit lung of a Goose. 



