400 HEAD AND NECK 



to the conchal region, and between it and the choanae, 

 is the naso-pharyngeal meatus (Fig. 155, i 7 ). 



Muco-periosteum of the Lateral Wall of the Cavuin Nasi. 

 It has been noted that the vestibule is lined with integument. 

 The remainder of the lateral wall, as well as the roof and floor 

 of the nasal fossa, is lined with mucous membrane which is 

 so closely blended with the subjacent periosteum that the 

 two are inseparable and form a muco -periosteum. This 

 is continuous through the naso-lacrimal duct with the ocular 

 conjunctiva, through the various apertures with the delicate 

 lining membrane of the air-cells which open into the nasal 

 cavity, and through the choanae with the pharyngeal mucous 

 membrane. On the lateral wall, as on the septum, the 

 muco-periosteum is mapped out into an upper olfactory and 

 a lower respiratory portion. This subdivision cannot be 

 appreciated by the naked eye, for the one district passes 

 into the other without any sharp line of demarcation. The 

 olfactory region comprises merely the upper concha; the 

 respiratory region includes the middle and inferior conchae, the 

 middle meatus, the lower meatus, and the atrium. In the lower 

 part of the lateral wall the muco-periosteum is thick and 

 spongy. This is particularly noticeable over the lower borders 

 and posterior extremities of the middle and inferior conchse, 

 where the membrane presents an irregular surface and forms 

 soft bulging cushions. This condition is largely due to the 

 presence of a rich venous plexus, the vessels of which run 

 for the most part in an antero-posterior direction. In the 

 case of the lower concha, the veins are so numerous 

 that the muco-periosteum assumes the character of cavernous 

 tissue, and is sometimes spoken of as the "erectile body." 

 When turgid with blood it swells out and obliterates the 

 interval between the concha and the septum. The muco- 

 periosteum of the floor, meatuses, and the atrium, is 

 smoother than, and not so thick as, that over the conchae. 

 Everywhere numerous mucous glands are embedded in it, 

 and the minute punctiform orifices of the ducts are visible to 

 the naked eye. In the olfactory region the lining membrane 

 of the nose, in the fresh state, is of a yellowish colour, and 

 it is softer and more delicate than in the respiratory part. 



The great vascularity of the mucous membrane of the nose 

 is doubtless for the purpose of moistening and raising the 

 temperature of the inspired air. 



