VERTEBRATE ANIMALS 



219 



canals, and on its side is a similar ridge indicating the horizontal 

 semicircular canal. The two ridges of the vertical canals on each 

 side converge to a median oval depression in the roof of the cranium 

 in which lie the two apertures o f the endolymphatic ducts (aqueduct! 



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vestibuli). In front of this region, again, the side of the cranium is 

 hollowed out slightly for the lodgment of the eyes or optic capsules, 

 so that it is termed the optic region. The hollowing is accentuated 

 by the roof and floor of the brain case, being carried out laterally 

 into flat wing-like expansions known as the supra- and infra-orbital 



