49^ THE ORGAN OF SMELL. 



Up to the present time it has been customary to cut sections in 

 celloidin ; but the combined celloidin-paraffin method may also be em- 

 ployed with good results, and even the paraffin method, if great care be 

 exercised in imbedding the tissue. 



The nerve-fibers and nerve-endings of the cochlea may be 

 stained with the chrome-silver method. For this purpose it is recom- 

 mended to employ embryos or young fetuses. 



X. THE ORGAN OF SMELL. 



THE nasal cavity consists of the vestibule, tbe respiratory region 

 with the accessory cavities, and the olfactory region. 



The vestibule is lined by stratified squamous epithelium. In 

 the region of the anterior nares are hairs, the sebaceous glands of 

 which are markedly developed, while at the level of the cartilage 

 mucous glands are also present. The stratified squamous epithe- 

 lium ceases at the anterior end of the inner turbinate bone and at 

 the inferior nasal duct. 



The respiratory region possesses a simple pseudostratified, 

 ciliated epithelium having two strata of nuclei and provided with 

 goblet cells ; the direction of the ciliate movement is toward the 

 posterior nares. Numerous leucocytes are usually found in the 

 epithelium and in the underlying mucosa. Branched alveolar 

 glands, having mucous and serous alveoli, are here present. Within 

 the mucosa are highly developed vascular plexuses, more especially 

 of a venous character. The accessory cavities are likewise lined 

 by ciliated epithelium, the ciliate movement being directed exter- 

 nally. 



The olfactory region is principally confined to the superior tur- 

 binate bone and to the nasal septum lying opposite, although in 

 the immediate vicinity of the olfactory region a few small islands of 

 the same epithelial type are found, either entirely isolated or con- 

 nected with the principal region by narrow bridges. In a fresh 

 condition the olfactory region may be differentiated from the sur- 

 rounding tissue by its color, which is distinctly yellow in man. 

 Its pigment is contained within the sustentacular cells described 

 on the next page. 



The epithelium of the olfactory region is of the columnar pseudo- 

 stratified type, with several strata of nuclei, and consequently 

 closely simulates a stratified columnar epithelium. Here we dis- 

 tinguish olfactory cells and sustentacular cells. 



The olfactory cells occupy a peculiar position among the cells 

 of special sense in that they represent true ganglion cells (Schultze, 

 Golgi, Ehrlich, Ramon y Cajal). Within the epithelial layer they 

 appear as spindle-shaped cells, with a spheric nucleus provided with 

 a large nucleolus lying in the thickest portion of each cell. The 

 nuclei of the different cells lie at varying levels in the middle stratum 



