330 



ZOOLOGY 



SECT. 



roof of the brain marking tlie anterior limit of the dien- 

 cephalon, is another commissure, the alcrrant commissure {c.ixp.), 

 which connects together the posterior and dorsal parts of the 

 parencephala ; this is not represented either in the Frog or 

 in hiohcr Vertebrates. The mid-hrain consists dorsally of two 



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oval o^/^/o Zo?>r.s {corpora Ugemina, Fig. 970, o. /.) and ventrally 

 of a mass of longitudinal nerve-fibres, the crura ccrelri (c. c), 

 passing forwards to the fore-brain. Each optic lobe contains a 

 cavity {optocKle) communicating with the iter, a narrow passage 

 leading from the diacoele to the metacoele. The cerebelhim (ch.) is, 

 like that of the Frog, of small size, being a small antero-posteriorly 



