THE EAR. 



717 



The utricle arises from that part of the vesicle which is in con- 

 nection with the semicircular canals. It is at first in direct con- 

 nection with the saccule, but after. a time it is only found to com- 

 municate by means of a narrow canal with a similar one from 

 the saccule ; these two canals are connected with a third, which 

 lies in the aqueductus vestibuli. 



FIG. 297. 



c.c 



Section through the head of a foetal sheep. (Boettcher.) R.V. Eecessus 

 vestibuli. v.B. Vertical semicircular canal. H.B. Horizontal semicircular 

 canal, o. Auditory ganglion, c.c. Canal of the cochlea. 



The canal of the cochlea is at first a straight tube, but as it 

 develops it becomes coiled upon itself. 



The walls of the primitive otic vesicle, formed from the epiblast, 

 become developed into the epithelium lining the internal ear. 

 The mesoblast immediately surrounding the vesicle forms a sup- 



