ORGANS OF SPECIAL SENSE 



295 



168). The condition shown in Fig. 173, at eleven days seven- 

 teen hours is substantially the same as in the adult. 



(d) Development of the Auditory Nerve and Sensory Areas of the 

 Labyrinth. During the changes in the form of the labyrinth 

 described in the preceding section, the lining epithelium has 

 become thin and flattened except in eight restricted areas: viz., 

 the three cristce acusticce, one in each of the ampullae of the semi- 

 circular canals, the macula utriculi, the macula sacculi, the 'papilla 



Fig. 173. — Model of the auditory labyrinth of 

 the right side of a chick embryo of 11 days 

 and 17 hours; external view. (After Rothig 

 and Brugsch.) Abbreviations as before. 



lagenoe, the papilla hasilaris and the macula neglecta. Each of 

 these contains sensory cells ending in fine sensory hairs project- 

 ing into the endolymph, or fluid of the labyrinth, and receives a 

 branch of the auditory nerve proceeding from the acustic ganglia. 

 Returning to an early stage to follow the development of sen- 

 sory areas and nerves, we note first that the acustic ganglion from 

 w^hich the auditory nerve arises takes its origin from the acustico- 



