228 THE RESPIRATORY SYSTEM 



accessory sinuses and is thickest where it covers the turbinal bones 

 and the adjacent portions of the nasal septum. The tunica pro- 

 pria is richly supplied with both mucous and serous glands. The 

 smaller ones, in the thinner portions of the mucous membrane, are 

 somewhat convoluted ; the larger and more numerous are tubulo- 

 acinar glands. Many of the latter are mixed glands containing 

 both mucous and serous acini. They produce an abundant secre- 

 tion. 



The Schneiderian membrane is in all portions extremely vas- 

 cular, many of its vessels having very thin walls. The thicker 

 portions over the turbinals and the septum are typically erectile. 

 The dense connective tissue of these portions is permeated with 

 broad venous channels which are surrounded by bands of smooth 

 muscle. Other muscular bundles are longitudinally distributed. 

 The small arteries are contained within the fibro-muscular 

 stroma. 



The subepithelial portion of the tunica intima contains fine 

 interlacing bundles of connective tissue and many capillary blood 

 vessels. Here and there it is also infiltrated with leucocytes and 

 occasional very minute lymphoid nodules are found. The lym- 

 phatics of the Schneiderian membrane lead posteriorly to the 

 lymphatic nodules of the naso-pharynx. 



The OLFACTORY PORTION of the nasal mucous membrane, 

 THE OLFACTORY ORGAN, lines the superior meat us, and its 

 irregular border here and there invades the upper portion of the 

 middle meatus. It consists of a fibrous tunica propria and a cloth- 

 ing of neuro-epithelium. The tunica propria contains elastic as 

 well as white connective tissue fibres, and many small tubulo- 

 acinar secreting glands, the olfactory glands of Bowman. Beneath 

 the epithelium is an indistinct basement membrane. 



The neuro-epithelium contains three intermingled cell types, 

 the sustentacular, olfactory, and basal cells. 



The Sustentacular Cells are columnar ciliated epithelial cells 

 which possess a distinct cuticular margin. Their nuclei are ovoid, 

 and, since they lie at the same level, they form a continuous su- 

 perficial zone of oval nuclei. The deep ends of the cells are often 

 branched ; they interlace with one another and with the processes 

 of the olfactory and basal cells. The cytoplasm of the susten- 

 tacular cells is finely granular and contains a yellow pigment. 



The Olfactory Cells occupy a unique position among neuro- 

 epithelial cells in that they are true nerve or ganglion cells. They 



