404 



ZOOLOGY 



contains an optocmle (Fig. 1046, o. v.) opening from a narrow 

 passage, the iter, which represents the original cavity of the 

 mid-brain. A further result of the extension of the hemi- 

 spheres and cerebellum respectively backwards and forwards is 

 that no part of the diencephalon (the.) appears externally except 

 on the ventral surface : elsewhere it is seen only when the 

 hemispheres are pressed aside. It contains a narrow vertical 



™Wrei 



Fn. 1045.— Columba livia. The brain; A, from abore; E, from below; C, from the left 

 side. c6. cerebellum ; c. h. cerebral hemispheres ; /. flocculus ; in/, infrmdibulum ; m. o. 

 medulla oblongata ; o. ^. optic lobes ; o. (. optic tracts ; 2jn. pineal body ; II — XIll, cerebral 

 nerves ; sp. 1, first spinal nerve. (From Parlcer's^ooiomy.) 



cavity, the diacceh ( V. 3), bounded laterally by the optic thalami, 

 and communicating on each side by the foramina of Monro 

 (/. m.) with the 2^'^^''^'^'^'^^^^ o^^ cavities of the hemispheres. 

 The corpora striata (c. s.) are of immense size, and form the 

 great mass of the hemispheres : the dorsal portions of the latter, 

 forming the roofs of the paracoeles, are very thin. Hippocampi 

 are absent. The anterior commissure is, as in lower Verte- 

 brates, the chief commissure of the fore-brain. The olfactory 

 hulhs (olf.) are extremely small, in correspondence with the poorly 



