Fig. 



121. — Vertical section through the cav- 

 ity of the nostril : rm, roof of mouth ; 

 opl, orbital plate ; cpl, cribriform plate. 



SENSE ORGANS. I go 



the skeleton it is largely, though not entirely, exposed. 

 It is bounded on each side by parts of the maxillary 



bone, and the orbital 

 plates of the ethmoid, 

 opl; above, it is sepa- 

 rated from the brain 

 cavity by a thin plate 

 perforated with many 

 holes — the cribriform 

 or colander plate of 

 the ethmoid, cpl — and 

 below, from the mouth 

 cavity, by the palatal 

 plates, which form the 

 roof of the mouth and 

 floor of the nasal cav- 

 ity, rm. It is divided 

 into two symmetric halves (right and left nostril) by 

 a bony septum, the 

 vomer, which is con- 

 tinued into the car- 

 tilaginous septum of 

 the nose. Each nos- 

 tril is again divided 

 by the turbinated or 

 scroll bones into an 

 upper and lower part, 

 which differ in struc- 

 ture and function. 

 The lower part is 

 comparatively sim- 

 ple, the upper part 

 complex; the one is 

 lined with the ordinary epithelium of the alimentary 

 passages, the other by a peculiar smooth epithelium. 



Fig. 122. — Vertical fore-and-aft section through 

 one nostril, showing the olfactory nerve 

 coming down from the olfactory lobe and 

 the nerve of feeling coming from behind. 



