378 



MJCROSCOriC A * ATOMY OF THE ORGANS. 



(1) The regio vestibularis is covered with a continuation of 

 the outer skin, which gradually takes on the character of a 

 mucous membrane. The outer layer is a stratified pavement 

 epithelium which contains hairs, sebaceous glands, and sweat 

 glands. A short distance from the outside, however, the hairs 

 and glands disappear, the epithelium becomes like that of a 

 mucous membrane, and mucous glands are found. 



(2) The transition from this region to the regio respiratoria 

 varies in different individuals. Usually it is marked by the 

 appearance of a layer of ciliated epithelial cells, the nuclei of 

 which are at various levels. Goblet cells are present in vary- 

 ing number. The connective-tissue tunica propria is thinner 

 in the accessory nasal cavities than- elsewhere. It contains 

 usually a great many leucocytes, which wander through the 

 epithelium into the nasal cavity. Branched tubular glands- 

 mucous, serous, and mixed are present. 



FIG. 274. 



Supporting cell- 



Bipolar 

 olfactory 

 cell 



Fibre of 

 olfactory 

 'nerve 



From a vertical section through the mucous membrane of the regio olfactoria of a quite 

 young dog. (Golgi's method.) X 450. 



(3) The regio olfactoria is distinguished from its surround- 

 ings by its yellow coloration. The olfactory epithelium char- 

 acteristic of this region is made up of a single layer of cylindri- 

 cal cells whose nuclei lie at different levels. Two kinds of cells 

 can be distinguished : the olfactory cells, and the supporting 

 cells (Fig. 274). 



The olfactory cells are peripherally placed, bipolar ganglion 

 cells, the bodies of which lie in the epithelial layer. The 



