THE NASAL CAVITIES. 



445 



Fig. 225. 



and is insinuated, by the middle meatus, into the cells of the inferior or 

 anterior compartment of these osteo-cartilaginous columns. It also penetrates, 

 by the semicircular opening of this meatus, into the sinus, to give it its 

 mucous covering, and is likewise prolonged into the apparatus of Jacobson. 

 Behind, it is confounded with the lining membrane of the pharyngeal cavity. 

 Its deep face is separated by the periosteum or perichondrium, from the 

 bony or cartilaginous walls on which it is spread ; and it is united to the 

 two precited layers, this union being closest where it is thinnest, although 

 it can always be easily distinguished from these two fibrous layers through- 

 out the whole extent of the nasal fossa. The free, or superficial face, presents 

 numerous glandular orifices, and is constantly covered by an abundance of 

 mucus, that prevents the desiccation to which this surface is exposed by 

 the incessant movement of air over it. 



Structure. — The organisation of the pituitary membrane resembles 

 that of other mucous membranes, but it also presents some differences 

 according as to whether it is examined near the nostrils or deeper in 

 the cavities. It is also usual to divide it into two portions : the olfactory 

 mucous membrane, which covers the upper part of the ethmoidal turbinated 

 bone and cells ; and the Sckneiderian memhrane covering the inferior two- 

 thirds of the nasal cavities. 



The cerium ol' the Schneiderian memhrane is thick, soft, spongy, and 

 rose-coloured, and contains a large number of vessels and glands. The 

 latter are mucous, or racemose glands, and are extremely abundant in tho 

 layer covering the septum of the nose, as well as at the inner face of the 

 cartilaginous appendices of the turbinated bones ; 

 though they are rare or altogether absent on the 

 external face of the latter. The epithelium is ciliated 

 and stratified, the deeper cells being round, those on 

 the surface columnar. 



The olfactory mucous membrane differs from the 

 preceding by its greater thinness, its delicateness, its 

 slightly yellow tint, and the character of its epithe- 

 lium. The cerium contains straight or slightly-con- 

 torted tubular glands — the glands of Bowman. The 

 epithelium is columnar and stratified, and readily 

 changes ; in animals it is destitute of cilia. The 

 deeper cells contain some yellowish pigment granules. 

 Schultze describes as olfactory cells, certain fusiform 

 elements which he considers as concerned in olfaction. 

 These cells have two prolongations a deep one, 

 which is connected with the fibres of the olfactory 

 nerve ; and a superficial, that enters between the 

 epithelial cells and tends to approach the free surface 

 of the membrane. 



(The " olfactory cells " are thin, rod-like bodies 

 (Pig. 225, 6), presenting varicose enlargements which 

 are connected with processes of deeper-seated nerve- 

 cells. The epithelial cylinders proper {d, e) are 

 related at their bases with the septa of connective 

 tissue belonging to the sub-epithelial glandular layer, 

 and are probably in communication with the olfactory 

 cell. Schultze describes another set of epithelial 

 cells (a) as teiminating externally by truncated flat surfaces, and to all 



is:r- 



CELLS OF THE OLFACTORY 



MUCOUS MEMBRANE. 



a, b, c, After Schultze , 

 d, e, f, After Locklinrt 

 Clarke. 



