806 



HEARING, SMELL, AND TASTE. 



SMELL. 



724. [The nasal fossae are two irregular cavities which communicate 

 anteriorly with the air through the anterior nares and posteriorly with the 

 pharynx through the posterior nares. The fossae are partially divided into 

 upper, middle, and lower air-passages or chambers by the superior, middle, 

 and inferior turbinated bones. They are lined by the Schneiderian or 

 pituitary mucous membrane, which is continuous anteriorly with the integu- 

 ment and posteriorly with the mucous membrane of the pharynx ; and with 

 the membrane lining the ducts and sinuses connected with the fossae. At the 

 position of the distribution of the olfactory nerve-filaments it is much 

 thicker, more vascular, pigmented, and lined by columnar nucleated epithe- 

 lial cells ; the remaining portion of the membrane covering the fossae, ex- 

 cepting near the anterior nares, is lined by columnar ciliated epithelium. 

 This membrane contains racemose mucous glands, which secrete mucus for 

 the purpose of keeping the membrane constantly moist, which is a condition 

 essential to perfect olfaction. 



725. The olfactory tract is a prolongation of the cerebrum, which ter- 

 minates anteriorly in a bulbous expansion, the olfactory ganglion. It consists 

 principally of gray matter. This ganglion rests upon the cribriform plate 



FIG. 198. 



FIG. 199. 



d e f 



FIG. 198. Vertical Section of Right Nasal Fossa, 

 showing Outer Side of Fossa. 1, olfactory tract; 2, ol- 

 factory nerves ; 3, middle turbinated bone ; 4, lower 

 turbinated bone ; 5, branches from the fifth nerve. 

 Branches of the fifth are also shown in the anterior 

 portion. (After Arnold.) 



FIG. 199. Cells of the Olfactory Mucous Membrane, 

 hart Clarke.) 



(a, 6, c, after Schultze ; d, e,f, after Lock- 



of the ethmoid bone, and in this position sends about twenty filaments, which 

 consist of gray matter alone, through the cribriform plate to be distributed to 

 the pituitary membrane of the upper third of the septum nasi, the upper 

 portion of the root of the nose, the superior, and a portion of the middle 

 turbinated bones. (Fig. 198.) The whole surface corresponding to the dis- 

 tribution of the olfactory nerve is colored brownish by the pigment in the 

 epithelial cells of the mucous glands and membrane. This pigmented region 

 is called the regio olfactoria, and is the essential portion of the nasal fossae 

 concerned in olfaction. 



726. According to Schultze, the epithelium of the regio olfartoria is 

 of two kinds: The first (Fig. 199, a) consists of yellow nucleated proto- 



