234 ANATOMY FOR NURSES [Chap. XIII 



These cavities ^ communicate with the air in front by the anterior 

 nares, or nostrils, while behind they open into the back of the 

 pharynx by the two posterior nares. 



The pituitary membrane (sometimes called the Schneiderian ^ 

 membrane) is the mucous lining of the nose. It closely covers 

 the nasal passages, and is thickest and most vascular over the 

 turbinated bones. 



Advantages of nasal breathing. — Under normal conditions 

 breathing should take place through the nose only (1) because the 

 arrangement of the turbinated bones makes the upper part of the 

 nasal passages very narrow ; (2) these passages are thickly lined, 

 and freely supplied with blood-vessels, so that they can, even in the 

 very coldest weather, moisten and warm the air before it reaches 

 the lungs; and (3) the presence of hairs at the entrance to the 

 nostrils serve as filters. 



Sinuses which communicate with the nose. — Opening into the 

 nasal cavities are minute channels which connect with (1) the 

 frontal sinuses, (2) the ethmoidal sinuses, (3) the maxillary 

 sinuses or antrums of Highmore, and (4) the sphenoidal sinuses. 

 The pituitary membrane is prolonged into these sinuses, and inflam- 

 matory processes in the nose may extend into these cavities. 



Mouth and pharynx. — As the mouth and pharynx are more 

 closely associated with the process of digestion rather than respira- 

 tion, they will be described with the digestive organs. The 

 mouth serves as a passageway for the entrance of air, and the 

 pharynx transmits the air from the nose or mouth to the larynx. 



RESPIRATORY SYSTEM 



Under this heading we group the organs which are concerned in 

 the process of respiration. In man they are as follows : — 



1. Larynx. 3. Bronchi. 



2. Trachea. 4. Lungs. 



1 Eleven bones enter into the formation of the nasal cavities : the floor is formed 

 by the palate (2) and part of the maxillse bones (2) ; the roof is chiefly formed by 

 the perforated plate of the ethmoid bono (1), the sphenoid (1), and by the (2) small 

 nasal bones ; in the outer walls we find, in addition to processes from other bones, 

 the two scroll-like turbinated bones (2). The vomer (1) forms part of the septum. 



* It was formerly supposed that the mucus secreted by the mucous membrane 

 of the nose came from the brain. Schneider was the name of the anatomist who 

 first disproved this. 



