NINTH LECTURE. 



THE RESPIRATORY ORGANS. 



472. The organs of respiration are, first, the Nose, which is divided 

 by a bony and cartilaginous septum (septum nasi) into two chambers — 

 the right and left nasal chambers ; secondly, the Larynx ; next the 

 Trachea, or windpipe ; trhen the Bronchi and Bronchial tubes ; 

 the Lungs ; the Thorax, or chest ; the Pleurae ; and the 

 Diaphragm. 



473. The Nasal Chambers (Plate XXXIIL, No. 3).— The right 

 and left nasal chambers of the horse each contain ttvo bones — one 

 above (the superior), and one below (the inferior). They are made up 

 of very fine sheets of bone, covered with mucous membrane, and 

 rolled up like a Turk's turban, and are called turbinated bones. 

 These bones give an extensive surface for the distribution of the 

 nerves concerned in the sense of smell, as well as for the ramification 

 of the blood-vessels which warm the air as it passes over their surface 

 to enter the windpipe. The membrane covering them clears the air 

 from solid particles of dust before it passes to the sinuses of the head 

 or, by way of the windpipe, to the lungs. The cow has three turbinated 

 bones in each chamber, also a canal (called Jacobson's canal) in the 

 floor of the nasal chamber, which communicates with the mouth. 

 The cavities in the horn cores of ruminants are also in communication 

 with the nasal chambers. 



474. The Larynx (Plate XXXIIL, No. 6) is situated at the back 

 of the throat, and is composed of five pieces of cartilage, or gristle, of 

 different shapes, which are so placed and joined that they are movable 

 on one another, thus regulating the inlet and outlet of the air. These 



