THE RESPIRATORY APPARATUS (Figs. 50 and 61, A) 



Owen says: " Notwithstanding the extent and activities of the 

 respiratory function in birds, the organs subservient thereto mani- 

 fest more of a reptilian than of the mammalian type of formation." 



By the action of the respiratory organs certain chemical and 

 physical changes take place in the blood. The chief of these con- 

 sists in absorption of oxygen from, and giving off carbon dioxid 

 to, the atmospheric air, the former changes being necessary for the 

 elaboration of the fluid, the latter for the elimination of a substance 

 which, if retained, would prove injurious. The organs of respira- 

 tion are invariably adapted to the wants of the animal and the me- 

 dium in which it lives. 



In the bird, which breathes through its nose, the organs of respi- 

 ration are nostrils, nasal chambers, pharynx, superior larynx, tra- 

 chea, inferior larynx, bronchi, bronchial tubes, lungs, and air-sacs. 



The Nostrils and the Nasal Chambers. The nostrils of the bird 

 open externally by two small elliptical openings, which pierce the 

 upper mandible. Within each nasal chamber (Fig. 26, A) are three 

 turbinated laminae, or turbinated bones. The inferior one is a sim- 

 ple fold adhering to the lower and anterior part of the nasal septum. 

 The middle turbinated bone is the largest. It is of infundibular 

 form, and adheres by its base to the septum and externally to the 

 side wall of the nose. It is convoluted with two and a half turns. 

 The superior bone, of bell shape, adheres superiorly to the frontal 

 bone. The internal turbinated bone extends toward the orbit; 

 the external terminates in a cul-de-sac behind the middle turbinal 

 (Fig. 26, No. A, i and 2, and G). 



The nostrils are separated by a partition which is partly bony and 

 partly cartilaginous. The posterior nares is represented by a long 

 slit in the hard palate. 



The Pharynx and the Superior Larynx. A transverse row of 

 horny, filiform papillae marks the anterior border of the pharynx, 

 where in other animals the soft palate, or velum, is located. (For 

 further description of the pharynx see special chapter.) 



The supero-posterior border of the larynx, at the juncture of the 



13 193 



