162 



PHYSIOLOGY 



CHAP. 



triangle, the apex being represented by the roof, and the base by 

 the floor of the nasal cavities. The median septum and the floor 

 are smooth, while the lateral walls are subdivided into three 

 irregular cavities or meatuses by the three turbinate bones. The 

 posterior ethmoid cells open into the superior meatus, the frontal 

 sinus, the median ethmoid cells and the maxillary antrum into 

 the middle meatus. The functional use of these bony cavities 

 and their communications with the rnuc'ous membrane of the 

 nasal fossae is quite unknown. 



The nasal cavities are divided into two regions: an upper, 

 known as the olfactory region, and a lower or respiratory region. 

 These can be distinguished by the eye, owing to their colour. In 

 the first the mucous membrane is yellowish (locus luteus), in the 



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XII 



FIG. 63. \ei\es nt" nns.il septum, seen from rijjht side. \. (Sappey, from Hirschfeld and 

 Leveille.) I, olfactory bulb; 1, olfactory nerves passing through foramina of cribriform plate, 

 ami desc-eiidm;.' t<> ! distributed on the septum ; 2, internal or septa! twig of nasal branch of 

 ophthalmic nerve ; M, naso-palatine nerves. 



second reddish (Schneider's membrane). Between the median 

 septum on the one hand and the upper and middle turbinals on 

 the other there is only a small fissure, the sulcus olfactorius or 

 olfactory groove. The respiratory region has a ciliated epithelium 

 and numerous acinous glands, while the olfactory region is covered 

 by an epithelium that has no hairs and is provided with tubular 

 glands. Fibres of the trigeminal nerve are not only distributed 

 all over the respiratory region of the nasal mucous membrane, but 

 also send branches to the olfactory region. 



The olfactory region is the part to which are distributed the 

 fibres of the olfactory nerve which take origin in the bulb of the 

 same name, traverse the pores of the cribriform plate of the 

 ethmoid bone, form a thick plexus with narrow elongated meshes, 

 and end in the mucous membrane of the upper third of the 

 septum, and the pars olfactoria of the upper turbinal (Figs. 

 63, 64). It was formerly believed that the olfactory region also 



