THE EAR. 



713 



the name of the otic vesicle. It soon becomes somewhat triangular 

 in shape, the base of the triangle lying upward. 



From the lower angle arises a projection, which is the rudi- 

 mentary canal of the cochlea. The angle lying next to the neural 

 epiblast similarly gives off a tubular process, which forms the 

 recessus vestibuli. 



FIG. 297. 



CJC 



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

 V.B. Vertical semicircular canal. H.B. Horizontal semicircular canal. G. Auditory 

 ganglion, c.c. Canal of the cochlea. 



Elevations in the primitive vesicle indicate the origin of the 

 semicircular canals, which become tubular, opening at their ends 

 into the general cavity of the vesicle. The two superior canals 

 are the first to appear, the horizontal canal rising somewhat 

 later. 



The part of the otic vesicle in connection with the canal of the 

 60 



