204 



COMPARATIVE ANATOMY 



after the embryonic period,^ and has plainly undergone a change of 

 function in connection with the perception of the warmth and 



moisture of the inspired air. 

 When well developed, it forms 

 a single or double coil, and 

 may even be more or less 

 branched (Fig. 164). Branches 

 of the trigeminal extend over 

 it, and supply its mucous mem- 

 brane. An olfactory and a 

 respiratory region can there- 

 fore also be distinguished in the 

 nasal chamber of Mammals. 



The nasal chamber usually 

 communicates with neighbour- 

 ing cavities, such as the maxil- 

 lary, frontal, and sphenoidal 

 sinuses (Fig. 163, B, c) : the 

 two last-mentioned cavities 

 arise in connection with the 



Fig. 163, a. — Lateral View of the 

 ISTasal Chamber or A Hdman Eji- 



BRYO. 



/, //, ///, the three olfactory ridges ; t, 

 supernumerary ridge whiclr occurs in 

 the embryo ; ii, tip of the nose 

 hard palate ; rr, base of skull ; 

 Eustachian aperture. 



OS, 



nasal apparatus, but may 

 lose their primary func- 

 tion, often persisting merely 

 as air-sinuses. 



The nasal glands may 

 be divided into two sets, 

 — numerous small, diffuse 

 Bowman's glands, and a 

 large gland of Stenson. 

 The latter appears early in 

 the embryo, and often be- 

 comes greatly reduced later 

 on in development ; it is 

 situated in the lateral or 

 basal walls of the nasal 

 cavity, and may extend 

 into the maxillary sinus 

 when the latter is well 

 developed. 



The appearance of an 

 external nose is very charac- 

 teristic of the olfactory or- 

 gan of Mammals : this must 



Fib. 163, b. — Sagittal Section through the 

 Nasaj^ and Bt'ocAL (.'avities of the 

 Human Head. 



be regarded as a derivative 

 of the outer chamber of the 

 nose of Reptiles and Birds. 



^ This is also true of the anterior 

 Mammals. 



/, //, ///, the three olfactoiy ridges ; sn'y 

 frontal sinus ; sit", sphenoidal sinus ; os, 

 aperture of Eustachian tube ; he, entrance- 

 to the mouth ; hj, tongue ; r. ;', atlas verte- 

 bra ; r. ('/, axis vertebra. 



(lower) ethmoid turbinal in microsmatie 



