AUDITORY ORGANS. 



521 



Shortly after the formation of the rudiment of the horizontal 

 semicircular canal a slight protuberance becomes apparent on the 



FIG. 303. SECTION OF THE HEAD OF A FCETAL SHEEP 20 MM. IN LENGTH. 



(After Bottcher.) 



R. V. recessus labyrinthi ; V.B. vertical semicircular canal ; H.B. horizontal semi- 

 circular canal; C.C. cochlear canal ; G. cochlear ganglion. 



inner commencement of the cochlear canal. A constriction arises 

 on each side of the protuberance, converting it into a prominent 

 hemispherical projection, the sacculus hemisphericus (fig. 304, 

 S.R\ 



The constrictions are so deep that the sacculus is only con- 

 nected with the cochlear canal on the one hand, and with the 

 general cavity of the auditory vesicle on the other, by, in each 

 case, a narrow though short canal. 



The former of these canals (fig. 304, b) is known as the canalis 

 reuniens. At this stage we may call the remaining cavity of the 

 original otic vesicle, into which all the above parts open, the utri- 

 culus. 



Soon after the formation of the sacculus hemisphericus, the 



