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- 

 geminal, and corresponds to 

 the lateral nasal gland of 

 Lizards. 



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 



FIG. 196A. LATERAL VIEW OF THE NASAL 



tip 



aperture ; pi, hard palate ; f, super- 

 numerary ridge (ectoturbinal) which 

 occurs in the embryo. 



CHAMBER ix THE HUMAN EMBRYO. 

 in the forms described above, 7> inferior (maxillarv) , //, middle> aild 



and consequently there is 7/7, superior turbinal ; cr, base of 



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 

 region 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, 

 situated in the posterior 

 or median parts of each 

 nasal chamber. The muc- 

 ous membrane covering 

 HUMAN HEAD. these contains olfactory 



7, inferior (maxillary), 77, middle, and 777, <* lls <f d is supplied by 

 superior turbinal ; he, entrance to mouth ; the olfactory nerve ; their 

 ly, tongue; ON, aperture of Eustachian skeletal Supports become 



sSs'^'U tb' &1S united later to theethmoid. 

 vertebra. In the respiratory portion, 



SAGITTAL SECTION THROUGH THE 

 AND HUCCAL CAVITIES OF THE 



