404 



ZOOLOGY 



SECT. 



contains an ojitoccde, (Fig. 1040, 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 cerebelhim respectively backwards and forwards is 

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

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

 hemispheres are pressed aside. It contains a narrow vertical 



Fi.;. 104'i. — Columba livia. The brain; A, from above; R, from below; C, from the left 

 side. eh. c<.reljullmii ; r.h. cerebral licuiispheres ; f. flocculus; inf. infundibulum ; tn.n. 

 medulla oblongata ; o. /. (ii)tic lobes ; o. <. oiitic tracts ; ;>». pineal body ; II — XI 11, cerebral 

 nerves ; sp. i, fir.st sjiinal nerve. (From Parker's Zootonu/.) 



cavity, the diaco'Ic (V. 3), bounded laterally by the optic thalami, 

 and communicating on each side by the foramina of Monro 

 (/.111.) with the pcracoeJcs or 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 pai^acceles, are very thin. Hippocampi 

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

 brates, the chief commissure of the fore-brain. The olfartor// 

 &h/&s (o//'.) are extremely small, in correspondence with the poorly 



