OLFACTOKY NERVES. 755 



are called the nasal fossae. The membrane lining these cavities is generally called the 

 Schneiderian mucous membrane, and sometimes, particularly by the French, the pituitary 

 membrane. This membrane is closely adherent to the fibrous coverings of the bones 

 and cartilages by which the nasal fossae are bounded, and it is thickest over the turbinated 

 bones. It is continuous with the membrane lining the pharynx, the nasal duct and lach- 

 rymal cauals, the Eustachian tube, the frontal, ethmoidal, and sphenoidal sinuses, and 

 the antrum. There are openings leading from the nasal fossae to all of these cavities. 



The essential organ of olfaction is the mucous membrane lining the upper half of the 

 nasal fossae. Not only has it been shown anatomically that this part only of the mem- 

 brane receives the terminal filaments of the olfactory nerves, but physiological experi- 

 ments have demonstrated that it is the only part capable of receiving odorous impressions. 

 If a tube be introduced into the nostril, placed horizontally over an odorous substance so 

 that the emanations cannot penetrate its caliber, no odor is perceived, though the parts 

 below the end of the tube might receive the emanations; but, if the tube be now directed 

 toward the odorous substance, so that the emanations can penetrate to the upper portion 

 of the nares, the odor is immediately appreciated. 



That portion of the lining of the nasal fossae properly called the olfactory membrane 

 extends from the cribriform plate of the ethmoid bone downward a little less than an 

 inch. It is exceedingly soft and friable, very vascular, thicker than the rest of the 

 Schneiderian membrane, and, in man, has rather a yellowish color. It is covered by 

 long, delicate, columnar cells, nucleated, each one provided with from three to eight cili- 

 ary processes, their movement being from before backward. The mucous glands of the 

 olfactory membrane are numerous, long, and racemose. They secrete a fluid which keeps 

 the surface moist, a condition essential to the accurate perception of odorous impressions. 



Physiological Anatomy of the Olfactory Nerves. The apparent origin of the olfactory 

 nerve is by three roots, from the inferior and internal portion of the anterior lobe of the 



FIG. 233. Olfactory ganglion and nerves. (Hirschfeld.) 



1, olfactory ganglion and nerves ; 2, branch of the nasal nerve; 3, spheno-palatine ganglion ; 4, 7, branches of the 

 great palatine nerve; 5, posterior palatine nerve; 6, middle palatine nerve; 8, 9, branches from the spheno-pala- 

 tine ganglion ; 10, 11, 12, Vidian nerve and its branches ; 13, external carotid branch from the superior cervical 

 ganglion. 



cerebrum, in front of the anterior perforated space. The three roots are an external and 

 an internal white root, and a middle root composed of gray matter. The external white 

 root is long and delicate, passing outward across the fissure of Sylvius to the middle lobe 

 of the cerebrum. The internal white root is thicker and shorter than the external root, 



