OLFACTORY ORGAN 



267 



The so-called external nasal gland of Birds is situated on the 

 frontal or nasal bones, along the upper margin of the orbit. It 

 is supplied by the first and 

 second branches of the tri- f 



geminal, and corresponds to 

 the lateral nasal gland of 

 Lizards. 



nr 



cr. 



OK. 



Fm. 196.\. LATERAL VIEW OF THE NASAL 

 CHAMBER IN THE HUMAN EMBRYO. 



7, inferior (maxillary), //, middle, and 

 ///, superior turbinal ; cr, base of 

 skull ; n, tip of nose ; ox, Eustachian 

 aperture ; pi, hard palate ; t, super- 

 numerary ridge (ectoturbinal) which 

 occurs in the embryo. 



Mammals. Correspond- 

 ing to the more marked de- 

 velopment of the facial por- 

 tion of the skull, the nasal 

 cavity of Mammals is propor- 

 tionately much larger than 

 in the forms described above, 

 and consequently there is 

 much more room for the ex- 

 tension of the turbinals. 

 These give rise to a spongy 

 labyrinth, with cell-like com- 

 partments lined by mucous membrane; and thus variously- 

 shaped projections, supported partly by cartilage and partly by 

 bone, are seen extending into the nasal cavity, and the olfactory 



organ reaches its highest 

 development amongst Ver- 

 tebrates. As in other ter- 

 restrial forms, however, a 

 posterior (upper) olfactory 

 vcgion of considerable ver- 

 tical extent, and an anterior 

 (lower) respiratory region 

 can be recognised, in each 

 of which turbinals, with 

 their skeletal supports, are 

 developed (Figs. 196-198). 

 In the olfactory region 

 are found a series of true 

 , \ -^ olfactory ridges, or scrolls, 



(\ \ ir ' 



ft \M 



situated in the posterior 

 or median parts of each 

 nasal chamber. The muc- 

 ous membrane covering 

 these contains olfactory 

 cells and is supplied by 

 the olfactory nerve ; their 

 skeletal supports become 

 united later to the ethmoid. 

 In the respiratory portion, 



OS. 



V. i. 



r. ii. 



Fit;. 196u. SAGITTAL SECTION THROUGH THE 

 L . NASAL AND BUCCAL CAVITIES OF THE 

 HUMAN HEAD. 



/. inferior (maxillary), //, middle, and ///, 

 superior turbinal ; lie, entrance to mouth ; 

 lij, tongue ; o-s, aperture of Eustachian 

 tube ; m', frontal sinus ; *.", sphenoidal 

 sinus; r.i, atlas vertebra; v.ii, axis 

 vertebra. 



