148 Journal .of Comparative Neurology 



and Chelonia on the other hand are recompensed for the absence 

 of any functional Jacobson's organ by the much greater com- 

 plexity of their nose proper. 



Jacobson's organ is very general in mammals especially ro- 

 dents, ruminants, perissodactyles, where it exists as a mere tube 

 ending blindly posteriorly and opening anteriorly into the 

 mouth by the ducts of Stenson (or naso-palatine canals). A 

 small depression on the median wall of the nasal pit in mammal- 

 ian embryos is the proton of Jacobson's organ. The external 

 nose of mammals is derivative of the outer chamber mentioned in 

 Caecilia. The Jacobson's organ of man lies high up, far above 

 the basales narium cartilage, which has its usual position. 



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