270 



COMPARATIVE ANATOMY 



but with the reduction of this sense, they lose their primary 

 function, often persisting merely as air-sinuses or even disap- 

 pearing entirely x (Pinnipedia). 



The nasal glands of Mammals may be divided into two sets, 

 numerous small, diffuse Bowman s glands, and a large Stensons 

 gland. The latter appears early in the embryo, and in many cases 



undergoes reduction ; it is 

 situated in the lateral or 

 basal walls of the nasal 

 cavity, opening into the 

 vestibule of the nose, and 

 may extend into the maxil- 

 lary sinus. 



The presence of an ex- 

 ternal nose (cf. p. 131), which 

 must be regarded as a de- 

 rivative of the outer nasal 

 chamber of Reptiles and 

 Birds, is very characteristic 

 of the olfactory organ of 

 certain Mammals, that of 

 Man being of a specialised 

 type not exactly comparable 

 to the so-called external 

 nose of other Mammals. 

 It is supported by an out- 

 ward extension of the nasal 



M 



FIG. 199. TRANSVERSE VERTICAL SECTION 



THROUGH THE NASAL CAVITY OF MAN. 



a, 6, c, inferior, middle, and superior nasal 

 passage ; C.cr, cranial cavity ; HG, hard 

 palate ; /, //, ///, inferior (maxillary), 

 middle, and superior turbinal ; J, J, 

 position of vestigial Jacobson's organs 



which are situated nearer the floor of the bones and by the cartila- 



cavity than is indicated in the figure ; M, ginous septum nasi which 

 maxilla; Or. wall of orbit; 8. septum c ,1 ,1 -, 



nasi ; SL, ethmoidal labyrinth ; *, point anses from the ethmoid, by 



at which the nasolacrymal duct opens ; the roofing lateral nasal 



t, entrance into the maxillary sinus ( C. m). cartilages connected with 



the septum, and by the 



vomer, as well as by other secondarily independent cartilages 

 (alinasals), which were primarily continuous with the general 

 solid cartilaginous wall, but become differentiated from the latter 

 in various ways in accordance with varied functional adaptations. 

 The outer nose contains a paired cavity (vestibule) continuous with 

 that of the olfactory chambers, and may be provided with a 

 complicated musculature, which in diving Mammals forms a 

 sphincter in connection with a special valvular apparatus for 

 closing the nostrils. An excessive development and increase in 

 the musculature, as well as an upward and backward shifting of 

 the nasal apertures in their relation to the skull, is seen in those 



1 The maxillary sinus is the most constant, and is typical for the Eutheria : 

 it usually extends into a number of neighbouring bones. In general, the pneu- 

 maticity of the skull is in direct proportion to the size of the animal : in Insecti- 

 vores and Bats the maxillary sinus is the only one present. 



