THE NASAL MUCOUS MEMBEANE. 



669 



Fis. 484. 



like that investing the cavity of the tympanum, with the periosteum 

 and perichondrium, over whicli it lies. It is continuous with the skin 

 through the nostrils ; with the mucous membrane of the pharynx 

 through the posterior apertures of the nasal fossae ; with the conjunctiva 

 through the nasal duct and lachrymal canaliculi ; and with the lining 

 membrane of the several sinuses which communicate with the nasal 

 fossas. The pituitary membrane, however, varies much in thickness, 

 vascularity, and general appearance in these diiferent parts. It is 

 ■thickest and most vascular over the turbinate bones (particularly the 

 inferior), from the most dependent parts of which it forms projections 

 in front and behind, thereby increasing the surface to some extent. On 

 the septum nasi the pituitary membrane is also very thick and spongy ; 

 but in the intervals between the turbinate bones, and over the floor of 

 the nasal fossa?, it is considerably thinner. In the maxillary, frontal, 

 and sphenoidal sinuses, and in the ethmoidal cells, the mucous lining 

 membrane, being very thin and pale, contrasts strongly with that 

 which occupies the nasal fossa?. 



In respect of the characters of the mucous 

 membrane, three regions of the nasal fossfe 

 may be distinguished. Thus, the region of 

 the external nostrils, including all the part 

 which is roofed by the nasal cartilages, is 

 lined with stratified squamous epithelium ; 

 and the remainder is divisible into two 

 parts, viz., the olfactory region in which 

 the epithelium is non-ciliated and columnar, 

 and the respiratory region in which, as also 

 in the sinuses, it is ciliated and columnar. 

 The membrane in the respiratory part, con- 

 sisting of the inferior turbinated and all the 

 lower portions of the fossa?, is studded with 

 numerous racemose mucous glands, which 

 open by orifices apparent on the surface. 

 These are most numerous about the middle 

 and hinder parts of the nasal fossae, and are 

 largest at the back of the septum near the 

 floor of the nasal cavity. They are much 

 smaller and less numerous in the membrane 

 lining the several cavities which communi- 

 cate with the nasal fossa?. 



Olfactory mucous niembrane. — The 

 olfactory region or that in which the 

 olfactory nerve is distributed, includes the 

 upper and middle turbinated parts of the 

 fossEe, and the upper portion of the septum. 



It is extremely vascular, a close plexus of large capillary vessels being 

 found under the lining membrane throughout its whole extent. Its 

 mucous membrane is thicker and more delicate in consistence than that 

 of the ciliated region, being soft and pnlpy. It has a distinct yellow 

 colour in man ; brown in some animals. The glands of this region 

 are numerous, but are of a more simple structure than those in the 

 lower part of the fossa? ; amongst them, however, some ordinary race- 

 mose glands are occasionally to be found The columnar cells on its 



Fi 



484.' — Vertical Section 

 op a small portion of the 

 Membrane of the Nose 

 FROM THE Olfactory Re- 

 gion (^Ecker). 50 Dia- 

 meters. 



«, coloured part of the epi- 

 thelium ; a', nuclei ; b, deeper 

 part containing the olfactory 

 cells ; c, connective tissue 

 of the mucous membrane ; d, 

 one of the glands ; d', its 

 duct ; e, twig of the olfactory 

 nerve ; e' small twig passing 

 towards the surface. 



