THE NASAL CAVITY 295 



above with the olfactory mucous membrane, and posteriorly with that 

 of the nasopharynx. The respiratory region is lined by columnar ciliated 

 epithelium of the pseudo-stratified type, which also contains many 

 mucus-secreting, goblet-cells. 



The epithelium rests upon a distinct basement membrane which 

 reacts to the specific stains for elastic tissue. The tunica propria 

 consists of a very vascular connective tissue; it varies much in thickness 

 in different portions. It is thinnest in the accessory sinuses and is thick- 

 est where it covers the turbinal bones and the adjacent portions of the 

 nasal septum. The tunica propria is richly supplied with both mucous 

 and serous glands. The smaller ones, in the thinner portions of the mu- 

 cous membrane, are somewhat convoluted; the larger and more numer- 

 ous are tubulo-acinar glands. Many of the latter are mixed glands con- 

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

 tion. 



The Schneiderian membrane is in all portions extremely vascular, 

 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 fibromuscular stroma. 



The subepithelial portion of the tunica propria contains fine inter- 

 lacing bundles of connective tissue and many capillary blood-vessels. 

 Here and there it is also infiltrated with lymphocytes and occasional 

 very minute solitary nodules are found. The lymphatics of the Schnei- 

 derian membrane lead posteriorly to the lymph nodules of the naso- 

 pharynx. 



THE ORGAN OF JACOBSON 



Associated with the respiratory portion is the rudimentary vomero- 

 nasal organ (of Jacobson). In the embryo of one month it appears as 

 a tubular extension, one on either side, into the corium of the median 

 septum, opening anteriorly. In transverse section it has a semicircular 

 outline, with its convexity mesial. In lower forms, e.g., Amphibia, it 

 persists in the adult as a functionally important organ concerned 

 with smell. It is innervated by fibers from the olfactory nerves, vomero- 

 nasal nerves, and by the nervus terminal-is, which is present also in man 

 (Johnston, Anat. Eec., 8, 4, 1914). In the cat the tall columnar ciliated 

 epithelium (pseudo-stratified) includes true sensory cells, similar to the 



