222 



ANATOMY FOR, NURSES. [CHAP. XIX. 



of the nasal cavities : the floor is formed by the palate and part 

 of the superior maxillary bones ; the roof is chiefly formed by 

 the perforated (cribriform) plate of the ethmoid bone, and by 



the two small nasal bones ; and 

 in the outer walls we find, 

 in addition to processes from 

 other bones, the three scroll- 

 like turbinated bones. The 

 turbinated bones, which are ex- 

 ceedingly light and spongy, 

 project into the nasal cavities, 

 and divide them into three 

 incomplete passages from be- 

 fore backwards, the supe- 

 rior, middle, and inferior me- 

 atus. The palate and superior 

 maxillary bones separate the 

 nasal and mouth cavities, and 

 FIG. 129. -VERTICAL LONGITUDINAL the cribriform plate of the eth- 



SECTION OF NASAL CAVITY. 1, olfactory r . . , 



nerve; v, branch of fifth nerve; h, hard moid forms the partition be- 



P alate - tween the cranial and nasal 



cavities. 



The mucous membrane (sometimes called the Schneiderian 1 

 membrane), which closely covers 'the nasal passages, is thick- 

 est and most vascular over the turbinated bones. In some 

 nasal troubles it becomes much thickened and swollen and 

 occludes the nasal passages to such an extent as to compel us 

 to breathe through the mouth. It contains numerous mucous 

 glands which secrete mucus for the purpose of keeping the 

 membrane moist, a condition which is essential to perfection 

 of the sense of smell. 



The mucous membrane lining the nasal chambers is supplied 

 with nerve-fibres from the first or olfactory nerve, and also with 

 fibres of common sensation from the fifth nerve. The fibres 

 from the olfactory nerves are distributed exclusively to the 

 upper air-passages of the nose, the mucous membrane of which 

 is covered with a specially modified epithelium. These fibres 



1 From Schneider, the first anatomist who showed that the secretions of the 

 nose proceeded from the mucous membrane, and not, as was formerly supposed, 

 from the brain. 



