OLFACTORY PIT 



OLFACTORY EPITHELIUM 



OLFACTORY NERVE 



Fig. 98. The origin and early development of 

 the olfactory organ. A thickening of the epidermis 

 forms the olfactory placode. The placode invagi- 

 nates and an olfactory pit is formed. Some of the 

 cells of the olfactory epithelium become nerve cells, 

 and their fibers form the olfactory nerve (first 

 cranial nerve). 



ENDOLYMPHATIC DUCT 



VIII GANGLION 



GANGLION 



HIND BRAIN 



Fig. 99. The origin and early develop- 

 ment of the internal ear. Left: The auditory 

 placodes form otic pits. The placode develops 

 in conjunction with the eighth cranial gan- 

 glion. Above: The otic vesicle becomes pear 

 shaped with the appearance of an outgrowth 

 which forms the endolymphatic duct. Later 

 nerve fibers connect the internal ear with the 

 hindbrain. 



