VOMERONASAL ORGAN 



93 



IS 



ered with an epithelium that resembles histologically the 

 respiratory epithehum of the nasal cavity. This lateral 

 epithelium may even be ciliated. The median wall is cov- 

 ered with an epithelium much Uke the olfactory epithelium 

 of the nose except that differentiated olfactory cells are 

 apparently not present. The cavity of the organ ' 

 sometimes obliterated by excessive 

 epithelial growth and calcareous con- 

 cretions may occur in its walls. As it 

 appears to be without nervous con- 

 nections, the vomero-nasal organ in 

 man is probably entirely rudimentary. 

 2. Comparative Anatomy. A vo- 

 mero-nasal organ has been recog- 

 nized for some time past in all classes 

 of vertebrates except the fishes, but, 

 according to Gawrilenko (1910), this 

 group too must be admitted to have at 

 least the foreshadowings of such an 

 organ. Even in such primitive forms 

 as the sharks and rays each olfactory 

 sac is divided into two compartments 

 with separate innervation and these two compartments 

 may be supposed to correspond one to the vomero-nasal 

 organ and the other to the olfactory organ proper. This 

 double character of the olfactory apparatus is also seen in 

 other fishes. Thus in the development of the olfactory sac 

 of the salmon Gawrilenko has shown that this organ 

 includes two sensory thickenings or placodes, a median 

 one and a lateral one. These two placodes can be 

 traced into the adult where they are said to give rise to 

 a mediaji olfactory area and a lateral area. The median 



Fig. 19. — Lateral view 

 of the head of a human 

 embryo showing the pore 

 (v) of the vomero-nasal 

 organ. After His, 1885, 

 Fig. 29. 



