204 



COMPARATIVE ANATOMY 



after the embryonic period, 1 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 



and 

 less 



single 



OS, 



FIG. 163, A. ^LATERAL VIEW OF THE 

 NASAL CHAMBER OF A HUMAN EM- 

 BRYO. 



/, //, ///, the three olfactory ridges ; f, 

 supernumerary ridge which occurs in 

 the embryo ; it, tip of the nose ; pi, 

 hard palate ; cr, base of skull 

 Eustachian aperture. 



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 

 Boivmans 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 

 be regarded as a derivative 

 of the outer chamber of the 



a single or double coil, 

 may even be more or 

 branched (Fig. 164). Branches 

 of the trigemiual 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 



FKJ. 163, B. SAGITTAL SECTION THROUGH THE 

 NASAL AND BUCCAL CAVITIES OF THE 

 HUMAN HEAD. 



/, //, ///, the three olfactory ridges ; sn', 

 Jrontal sinus ; an", sphenoidal sinus ; o-s, 

 aperture of Eustachian tube ; be, entrance 

 to the mouth ; Ig, tongue ; ?:. i, atlas verte- 

 bra ; v.ii, axis vertebra. 



nose of Reptiles and Birds. 



1 This is also true of the anterior (lower) ethmoid turbinal in microsmatic 

 Mammals. 



