CHAP. XVI.] THE SCHNEIDERIAN MEMBRANE. 3 



ately within the nostrils is a growth of strong hairs, or vibrissce, 

 designed to obstruct the entrance of injurious substances. 



With regard to the interior of the nose, its cavities are formed 

 of bone, generally thin, compact, and laminated, everywhere in- 

 vested with periosteum. This latter is lined with mucous mem- 

 brane, the fichneiderian or pituitary membrane, continuous with the 

 skin of the face at the nostrils, with the mucous covering of the eye 

 through the lachrymal passages, and with that of the pharnyx and 

 middle ear through the posterior nares. 



The mucous membrane of the nose varies in its structure in dif- 

 ferent regions. In many situations, especially in the sinuses, it is 

 so intimately connected with the periosteum that that fibrous mem- 

 brane is in fact a submucous areolar tissue ; and the entire lining of 

 the bone has been sometimes called a fibro-mucous membrane, which, 

 as a whole, is delicate in the extreme. On the septum and spongy 

 bones, bounding the direct passage from the nostrils to the throat, 

 the lining membrane is much more thick, partly in consequence of a 

 multitude of glands being disseminated beneath it, and opening 

 upon it, but chiefly perhaps from the presence of ample and capa- 

 cious submucous plexuses of both arteries and veins, of which the 

 latter are by far the more large and tortuous. These plexuses, 

 lying, as they do, in a region exposed more than any other to ex- 

 ternal cooling influences, appear to be designed to promote the 

 warmth of the part, and to elevate the temperature of the air on 

 its passage to the lungs. They also serve to explain the tendency 

 to hemorrhage from the nose in cases of general or local plethora. 



In the vicinity of the nostrils the mucous membrane exhibits pa- 

 pillae, and a scaly epithelium, like the corresponding parts of the 

 skin. In the sinuses and in all the lower region of the nose, the 

 epithelium is of extreme delicacy, being of the columnar variety, 

 and clothed with cilia. This being the first occasion on which we 

 have had to speak of this kind of epithelium, we shall briefly de- 

 scribe its structure and mode of growth. 



The nucleated particles of which it consists are found* in a double 

 series: of which the first, resting on the subjacent basement tissue, 

 is as yet imperfect; and the second, rising to and forming the free 

 external surface of the membrane, is completely developed, and 

 furnished with cilia. The deeper series is the more adherent, and 

 if recent will be found to remain more or less attached, when the 

 superficial and perfect layer has been removed by a gentle stream of 

 water. It will then have the appearance represented at b, fig. 103. 

 The nuclei, which are arranged nearly on the same level, are ovoid, 



B2 



