NASAL CAVITY 



805 



Central 



processes of 



olfactory 



Olfactory 

 hairs 



Peripheral 

 process 



Body of 

 cell with 

 nucleus 



Central 

 process 



FIG. 676. OLFACTORY AND SUPPORTING CELLS. 



for some distance as attenuated or branched processes. These cells contain 

 elliptical or oval nuclei, which are situated at the deep ends of the columnar 

 parts of the cells, and' form what is termed the zone of oval nuclei. In many 

 animals the free surface 

 of this columnar epithel- 

 ium is covered byia thin 

 limiting membrane. 



2. Olfactory Cells. 

 These are bipolar 



nerve -cells, the central 

 processes of which are 

 continued as the axons 

 of the olfactory nerve- 

 fibres. They are homo- 

 logous with the cells of 

 the spinal ganglia, but 

 differ from them in that 

 they retain their primi- 

 tive position in the sur- 

 face epithelium. The 

 cell bodies are spindle- 

 shaped and are arranged 

 in several rows between 

 the deeper, attenuated 

 parts of the supporting 

 cells. Each consists of 

 a large, spherical nucleus 

 with a small amount of 

 enveloping protoplasm ; 

 the nuclei form a layer of some thickness, termed the zone of round nuclei. The 

 peripheral process of each cell is rod-like, and extends between the columnar 

 portions of the supporting cells as far as their free surfaces, where it pierces the 

 external limiting membrane and divides into a number of fine hair-like processes, 

 termed olfactory hairs. The central process is a delicate, beaded filament, and is 

 continued upwards as the axon of an olfactory nerve-fibre. 



3. Basal Cells. These cells are branched, and lie on a basement membrane 

 between the deep extremities of the supporting and olfactory cells. 



Olfactory Nerves. The fibres of the olfactory nerves are devoid of medullary 

 sheaths, and arise, as stated, from the olfactory cells. They are collected into 

 fasciculi which form a plexiform network under the mucous membrane and ascend 

 on the medial and lateral walls of the olfactory region of the nasal cavity. They 

 are lodged, near the base of the skull, in grooves or canals in the ethmoid bone and 

 pass into the cranial cavity through the foramina in the lamina cribrosa of the 

 ethmoid. Immediately above the lamina cribrosa they enter the olfactory bulb, in 

 the glomerular layer of which they subdivide and form synapses with the dendrites 

 of the mitral cells of the bulb. 



The trigeminal nerve supplies branches of ordinary sensation to the nasal mucous membrane 

 as follows : The septum is chiefly supplied by the naso-palatine nerve, but its posterior part 

 receives 'some filaments from the spheno-palatine ganglion and from the nerve of the pterygoid 

 canal, and its anterior portion from the naso-ciliary branch of the ophthalmic. The lateral 

 wall is supplied (1) by the upper nasal branches of the nerve of the pterygoid canal and from 

 the spheno-palatine ganglion ; (2) by the lower nasal branches derived from the anterior palatine ; 

 and in front by (3) the naso-ciliary branch of the ophthalmic. The floor and anterior part of the 

 inferior meatus are supplied by a nasal branch of the anterior superior alveolar nerve. 



Blood-vessels. Arteries. The chief artery of the nose is the spheno-palatine branch of the 



internal maxillary artery. This reaches the nasal cavity through the spheno-palatine foramen, and 



divides into (a) posterior nasal, which ramifies over the meatuses and conch ae and sends branches 



to the maxillary and frontal sinuses and the ethmoidal cells ; and (6) naso-palatine, the artery 



' the septum. Twigs are given to the upper portion of the cavity by the anterior and posterior 



thmpidal arteries, while its posterior part receives some small branches from the descending 



palatine. The nostrils are supplied by the lateral nasal branch of the external maxillary, and by 



