136 



DISSECTION OF THE NASAL CAVITY. 



vessels ; but the apertures that lead to the sinuses and the orbit are only 

 somewhat diminished by the lining they receive. The membrane is 

 stretched over the opening of the ductus ad nasum, forming a flap or valve 

 to close the aperture. 



Tho characters of the membrane in the lower or respiratory part of the 

 nose differ greatly from those of the same layer in the olfactorial region 

 near the roof. 



In the lower region of the nose, through which the air passes to the 

 lungs, the membrane is thick, and closely united to the subjacent perios- 

 teum and perichondrium ; and on the margins of the two inferior spongy 

 bones it is projected somewhat by the large submucous vessels, so as to 

 increase the extent of surface. In the canals and sinuses it is very thin. 

 Near the nostril it is furnished with papilla?, and small hairs (vibrissaj). 



The surface is covered by the apertures of branched mucous glands, 

 which are in greatest abundance, and of largest size, about the middle and 

 posterior parts of the nasal fossa. In the lower part of the nose, and in 

 the sinuses, the epithelium is of the columnar ciliated kind; but it becomes 

 laminated or scaly in the dilatation or vestibule inside the nostril (tig. 

 31, 10 ). 



Fig. 32. 



A. 1. Columnar epithelium at the free surface. 



2. Granular or middle layer of the same. 



3. Deepest layer of elongated cells placed vertically. 



4. Secreting tubular glands. 



B. a. Pieces of the columnar epithelium greatly en- 



larged. 



ft. Olfactorial cells amongst the epithelium parti- 

 cles. 



MAGNIFIED VERTICAL SECTION OF THE Mucous MEMBRANE OF THE NOSE (altered from Henle). 



The olfactory region (fig. 32) is situate at the top of the nasal cavity, 

 and is confined to the surface of the roof formed by the cribriform plate of 

 the ethmoid; to a portion of the outer wall constructed by the lateral 

 mass of the ethmoid bone: and to a corresponding extent of the septum, 

 vi/., about one-third. 



The mucous membrane in the olfactory region receives the olfactory 

 nerve, and is therefore the seat of the sense of smell. It differs much 

 from that in the lower portion of the nose, for it is less strong and vascu- 

 lar; and is of a yellowish color, which is due to pigment in the epithelium 

 and the glands. 



The epithelium (fig. 32 A) is thicker but softer here than lower in the 

 cavity, and it is columnar on the surface, but not ciliated. Beneath the 



