CHAPTER II. 



THE NASAL CAVITIES AND OLFACTOEY STEUCTUEES. 



In tracing the development of structures subservient to the sense 

 of smell, the following elements have to be dealt with : 



(1) The olfactory sense epithelium and olfactory nerves ; 



(2) The parts of the brain concerned with the sense of smell, 

 so far as we know them ; 



(3) The capsule which contains the olfactory epithelium ; 



(4) The respiratory tract of the nasal cavities. 



lat. nas. proc. 

 mes. nas. proc. 



olfactory pit and plate 



for Jacobson's organ 

 stomodaeum 



Fig. 16.— The Olfactory Pit and Nasal Processes in a 4th week human embryo 

 (After Kollmann.) 



(1) Origin of the Olfactory Sense Epithelium. — A small 

 area of the epiblastic cells, lying under the fore-brain becomes 

 demarcated on each side, to form the olfactory plates. Around 

 these two plates the lateral and mesial nasal processes grow up 



