1208 



THE RESPIRATORY SYSTEM 



openings which are seen in the bony walls; those apertures, however, which 

 lead into the paranasal-sinuses and into the naso-lacrimal duct remain patent, 

 although as already stated the bony openings are much reduced in size. 



In the nasal cavity the bright rose-red vascular mucous membrane is tightly bound to the 

 periosteum and perichondrium, and is covered with a ciliated columnar epithelium. Numerous 

 large mucous nasal glands [glandulse nasales] pour their more or less watery secretion over the 

 entire surface. A very considerable venous plexus is found in many parts of the nasal mucosa. 

 Over the inferior concha and to a less extent in the mucosa of the middle and superior conchae, 

 it forms the cavernous plexuses of the conchas [plexus cavernosi concharum] contributing to 

 build up about these bodies a true erectile tissue. The thickness which these glands and venous 

 plexuses give to the mucous membrane of the conchae causes the marked increase in size of 

 these bodies over that of their bony supports. The region covered by the mucous membrane 

 just described forms the greater part of the nasal cavity, and is known as the respiratory region 

 [regio respiratoria]. The mucous membrane of a small area over the superior concha and the 

 adjacent septal wall (fig. 969) has a somewhat dilTerent structure. In this area the oKactor)' 

 nerves are distributed, whence it is known as the olfactory region [regio olfactoria] and its mucous 

 membrane, compared with that of the respiratory region, is less vascular, yellow or yellowish- 

 brown in colour, and covered by a non-ciliated epithelium. Its cells, specially modified, some 

 of which are directly connected with the olfactory nerve, form the olfactory organ [organon 

 olfactus]. Small mucous olfactory glands [glandula? olfactorise] occur in the region. The 

 mucous membrane which lines the paranasal sinuses throughout is a continuation of the nasal 

 mucosa; it is, however, paler, less vascular, somewhat thinner, and more loosely attached to 

 the bones. Mucous glands are numerous. 



The waving of the cilia in the nasal cavity is such as to sweep foreign matter toward the 

 choanse; in the paranasal sinuses, toward the nasal cavity. 



Fig. 969. — Diagram of the Distribution op the Nerves in the Nasal Cavity. (Poirier 



and Charpy.) 



The olfactory area is represented by dots. 



Posterior superior nasal 



Posterior su- 

 Anterior perior nasal 

 ethmoid ant. pal. 







Posterior 

 inferior nasai 



Anterior 

 palatine 



Vessels and nerves. — The arteries of the nasal cavity are the spheno-palatine artery from 

 the internal maxillary which, through its posterior lateral nasal branches, supplies the middle 

 and inferior concha; (p. 549), the anterior and posterior ethmoidal arteries from the ophthalmic 

 (p. 553), the descending palatine artery from the internal ma.xillary (p. 549), and the superior 

 labial branch of the external maxillary to the vestibule. The venous plexuses of the mucous 

 membrane are drained posteriorly by the spheno-palatine to join the pterygoid plexus, superiorly 

 by the anterior and posterior ethmoidal veins to join the superior ophthalmic vein, and ante- 

 riorly by small branches to join the facial. The lymphatics form a well-developed plexus which 

 is said to comnmnicate indirectly, through the lymphatics surrounding the olfactory nerves, 

 with the subdural and subarachnoid spaces. Posteriorly two or more well-developed trunks 

 cominunicato with the pharj^ngeal lymphatics, and anteriorly the nasal lymphatics join with 

 the lyniphatios of the face. The olfactory nerves pass through the cribriform plate of the 

 ethmoid bone and are distributed to the olfactory area (p. 929). The trigeminal nerve furnishes 

 the following branches to the nasal cavity: — branches from the naso-ciliary brancli of the oph- 

 thalmic nerve; the Vidian nerve; the posterior superior and posterior inferior nasal and the ante- 

 rior palatine from the spheno-jjalatine ganglion (p. 962); the anterior superior alveolar from the 

 infra-orbital division of the maxillary nerve (p. 91.^8). 



The development of the nose. — The nasal cavity makes its appearance as a depression of 

 the ectoderm on either side of the median line, immediately in front of the oral fossa, with 

 which the depressions arc at first contituious. Later, by the union of the maxillary and globular 

 processes (see p. 18), the de[)re.ssions arc separated from the anterior part of the oral fossa, and 

 this separation is continued l)y the formation of the palatal processes of the maxilUe and palatine 

 bones, so that finally the nasal cavities communicate posteriorly only with the pharynx. 



The cartilage which forms the latenil walls of the nasal fossic is at first quite smooth, but 

 later it beconxis crod(!d by ab.sorption, whereby the nasal concha* are formed. The erosion also 

 extends into the ethmoid bone, forming the ethmoidal cells, and into the neighbouring bones 

 to form the frontal, sphenoidal, and nuixillary sinuses. 



