888 



THE ORGANS OF SENSE. 



a projecting fold of mucous membrane, and the orifice of the antrum is contracted 

 to a small circular aperture, much narrower than in the skeleton. 



In the inferior meatus the orifice of the nasal duct is partially hidden by either 

 a single or double valvular mucous fold, and the anterior palatine canal either 

 completely closed in or a tubular cul-de-sac of mucous membrane is continued a 

 short distance into it. This cul-de-sac is termed the organ of Jacobson, and is 

 present in all mammals as well as man. In the former it consists of a bilateral 

 tube, situated in the nasal septum and supported by hyaline cartilage, the cartilage 

 of Jacobson. 



In the roof the opening leading to the sphenoidal sinus is narrowed, and the 

 apertures in the cribriform plate of the ethmoid completely closed in. 



Structure of the Mucous Membrane. The epithelium covering the mucous 

 membrane differs in its character according to the functions of the part of the 

 nose in which it is found. Near the orifice of the nostril, the vestibule, where 

 common sensation is chiefly or alone required, the epithelium is of the ordinary 

 pavement or scaly variety. In the rest of the cavity, below the distribution of the 



Middle meatus, 



Infundibulum 

 Opening of nasal duct 



Anterior ethmoid cells 



nj 



Floor of orbft-Sjwyjit 



F 



Middle ethmoid cells > 



Post, ethmoid 

 cells 



FIG. 525. Horizontal section, high up, of the nasal fossae, viewed from above. (Cryer.) 



olfactory nerves i. e. in the respiratory portion of the nasal cavity the epithelium 

 is columnar and ciliated. This is the case also in the meatuses of the nose. In 

 this region, beneath the epithelium and its basement membrane, is a fibrous layer 

 infiltrated with lymph-corpuscles, so as to form in many parts a diffuse adenoid 

 tissue, and beneath this a nearly continuous layer of smaller and larger glands, 

 some mucous and some serous, the ducts of which open upon the surface. In the 

 olfactory region i.e. the region in which the terminal filaments from the olfactory 

 nerves are distributed (see page 889) the epithelial cells are columnar and, for the 

 most part, non-ciliated : their free surface presents a sharp outline, and their deep 

 extremity is prolonged into a process which runs inward, branching to commu- 

 nicate with similar processes from neighboring cells, so as to form a network in 

 the deep part of the mucous membrane. Lying between them are cells (termed by 

 Max Schultze, olfactory cells], which consist of a nucleated body and two processes, 

 of which one runs outward between the columnar epithelial cells and projects on 

 the surface of the mucous membrane ; the other (the deep) process runs inward, 

 is frequently beaded like a nerve-fibre, and is believed by most observers to be in 

 connection with one of the terminal filaments of the olfactory nerve. Amongst 



