THE NASAL FOSSAE. 



821 



narrower, and the turbinated bones, especially the lower ones, appear larger and 

 more prominent than in the skeleton. From the same circumstance also the 

 various apertures communicating with the meatuses are considerably narrowed or 

 completely closed. 



The vestibule is lined by modified skin, and contains hairs or vibrissse which 

 guard the entrance of the nostril. 



Structure of the Mucous Membrane. The epithelium covering the mucous 

 membrane differs in its character according to the functions of the part of the nose 

 in which it is found. In the respiratory portion of the nasal cavity the epithelium 

 is columnar and ciliated. Interspersed among the columnar ciliated cells are 

 goblet or mucin cells, while between their bases are found smaller pyramidal cells. 

 In this region, beneath the epithelium and its basement membrane, is a fibrous 



Eye-ball 



(Groove (hiatus semilunaris) 

 leading to infundibulum 

 Middle turbinated bone 



Middle meatus 

 Antrum of Highmore 

 Inferior meatus 



Inferior turbinated bone 



f Buccal cavity 



\ Space between cheek and gum 

 'Molar tooth, upper jaw 



Root of molar tooth 



Inferior dental nerve 



PIG. 437. Transverse vertical section of the nasal fossae. The section is made anterior to the superior 

 turbinated bones. (Cryer.) 



layer infiltrated with lymph-corpuscles, so as to form in many parts a diffuse 

 adenoid tissue, and beneath this a nearly continuous layer of smaller and larger 

 glands, some mucous and some serous, the ducts of which open upon the surface. 

 In the olfactory region the mucous membrane is yellowish in color and the epi- 

 thelial cells are columnar and non-ciliated; they are of two kinds, supporting* 

 cells and olfactory cells. The supporting cells contain oval nuclei, situated in the 

 deeper parts of the cells : the free surface of each cell presents a sharp outline, 

 and its deep extremity is prolonged into a process which runs inward, branching 

 to communicate with similar processes from neighboring cells, so as to form a net- 

 work in the deep part of the mucous membrane. Lying between these central 

 processes of the supporting cells are a large number of spindle-shaped cells, the 

 olfactory cells, which consist of a large spherical nucleus surrounded by a small 



