THE ORGANS OF SPECIAL SENSE 



externally with the skin through the anterior nares, and with the mucous mem- 

 brane of the nasopharynx through the posterior nares. From the nasal fossae 

 its continuity may be traced with the conjunctiva through the nasal duct and 

 lacrimal canals; with the lining membrane of the tympanum and mastoid cells 

 through the Eustachian tube; and with the frontal, ethmoidal, and sphenoidal 

 sinuses, and the maxillary sinus through the several openings in the meatuses. 

 The mucous membrane is thickest and most vascular over the turbinated bones. 

 It is also thick over the septum, but in the intervals between the spongy bones and 

 on the floor of the nasal fossa? it is very thin. Where it lines the various sinuses 

 it is thin and pale. 



Owing to the great thickness of this membrane, the nasal fossa? are much 

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

 more prominent than in the dried skull. From the same circumstance, also, the 

 various apertures communicating with the meatuses are considerably narrowed. 



EPITHELIUM 



GLANDS OF 



BOWMAN 



FIG. 793. Section of the olfactory mucous membrane. fCadiat.) 



Structure of the Mucous Membrane (Fig. 793). 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, 

 which is also the type found in the accessory sinuses, with the exception of the maxillary, where 

 the epithelium is of the simple polygonal variety. 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 layer infiltrated 

 with leukocytes, so as to form in many parts diffuse lymphoid tissue, which is particularly plentiful 

 in children; beneath this is a nearly continuous layer of smaller and larger glands, some mucous 

 and some serous, the ducts of which open upon the surface. In the respiratory portion of the 

 mucous membrane there is an extensive anastomosing plexus of veins, which in some regions 

 forms a distinct cavernous tissue (plexus cavernosus concharum). The cavernous tissue is 

 particularly distinct over the inferior turbinated bones. In the olfactory region the mucous 

 membrane is yellowish in color and the epithelial cells are columnar and non-ciliated; they are 

 of two kinds, supporting cells and olfactory cells. 



The supporting cells are irregular pigmented elements that 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 network in the deep part of the mucous mem- 

 brane. 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 amount of granular protoplasm, and possessing two processes, of which one runs 

 outward between the columnar epithelial cells, and projects on the surface of the mucous mem- 

 brane as a fine, hair-like process, the olfactory hair; the other or deep process runs inward, is 

 frequently beaded, and is continuous with one of the filaments of the olfactory nerves. Beneath 

 the epithelium, extending through the thickness of the mucous membrane, is a layer of tubular, 



