XII.J 



THE NASAL ORGAN. 



399 



to the fenestra ovalis. These ossicles, which arise 

 mainly from the mandibular and hyoid arches (vide 

 p. 403), are at first imbedded in the connective tissue in 

 the neighbourhood of the tympanic cavity, but on the 

 full development of this cavity, become apparently 

 placed within it, though really enveloped in the mucous 

 membrane lining it. 



Nasal organ. In Mammalia the general formation 

 of the anterior and posterior nares is the same as in 

 Birds; but an outgrowth from the inner side of the 

 canal between the two openings arises at an early period ; 

 and becoming separate from the posterior nares and 

 provided with a special opening into the mouth, forms 

 the organ of Jacobson. The general relations of this 

 organ when fully formed are shewn in Fig. 133. 



Fig. 133. 



Section through the Nasal Cavity and Jacobson's Organ. 

 (From Gegenbaur.) 



sn. septum nasi ; on. nasal cavity ; J. Jacobson's organ ; d. edge 

 of upper jaw. 



