AUDITORY ORGANS. 



521 



Shortly after the formation of the rudiment of the horizontal 

 semicircular canal a slight protuberance becomes apparent on the 



JIB 



c.c 



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



(After Bottcher.) 



A. 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 



