142 TEE RESPIRATORY SYSTEM. 



third of the septum, the roof of the nose, the superior and part 

 of the middle turbinated bone, and the ethmoid in front of 

 them. The remainder of the nasal fossae and the accessory 

 sinuses (maxillary, ethmoidal, sphenoidal, frontal) are covered 

 by the respiratory portion of the mucosa. 



The respiratory portion of the nasal mucous membrane, like 

 the air-passages in general, is lined with stratified ciliated 

 epithelium, among which are occasional goblet-cells. The 

 epithelium rests on a firm tunica propria, beneath which is a 

 variable amount of loose submucous areolar and connective 

 tissue. The submucosa contains abundant and ample blood- 

 vessels, nodules and diffuse masses of lymphoid tissue, and 

 small racemose mucous glands with ducts lined by columnar 

 epithelium, gradually merging into the ciliated cells of the 

 surface. The vascularity of this region explains the fre- 

 quency of nosebleed. Over the septum and turbinated bones 

 the mucous membrane is thick, very vascular, and contains 

 large numbers of the glands ; in the accessory sinuses it is 

 thin and less glandular and vascular. 



The olfactory portion of the nasal mucous membrane con- 

 tains the nerve-terminals for the sense of smell. It is thick, 

 and mostly pigmented, of a yellowish color. Its superficial 

 layer is composed of stratified columnar non-ciliated epithe- 

 lium. The surface-cells are of two kinds, sustentacular and 

 olfactory. 



The sustentacular or supporting cells are long columnar cells, 

 with deeply placed oval nuclei ; their deep portions are 

 branched and irregular, their free extremities are granular 

 and exhibit the appearance of a superficial covering cuticle. 



The olfactory cells are slender, elongated, linear cells, with 

 large spherical nuclei which cause a marked bulbous swelling 

 of the cell-body. They lie between the supporting cells, and 

 are a form of neuro-epithelium, or, perhaps, actual nerve- 

 cells. Their lower extremities are continuous with, or at least 

 in intimate relation with, terminal filaments of the olfactory 

 nerve. Their prominent round nuclei form a zone in the 

 lower portion of the epithelial layer. The lowest epithelium- 

 cells are spheroidal and germinal. 



The epithelium rests upon a connective-tissue layer, the 

 tunica propria and submucosa, which contain the terminal 



