UIGU SCHOOL ZOOLOGY. 



31 



35. Transections of the 

 bi-ain show that it is a 

 tube, the walls of which 

 are thick in some parts 

 and thin in others, and 

 the cavity of which is 

 dilated into ventricles, 

 communicating with 

 each other. The roof of 

 the cerebral legion is so 

 thin that the functions 

 that are discharged by it 

 in the higher animals, 

 must have their seat else- 

 where in the fish. A 



similar condition is ob- 

 A. a. 



Fiy. 11.— Brain of Catfish. served in the thalamic 



A- From above. B-From below. region, and that of the 

 Rh, olfactory lobes; Ot, olfactorj- tracts; Pr, , ,, 



cerebral hemispheres ; Mes, optic lobes ; Cb, cere- medulla oblongata, (ex- 

 bellum ; Slet, meilulla oblon<rata ; a and c, trigem- _ ° ^ 



iiial and vaj,'al lobes of medulla ; b, inferior lobes of cent ailteriOl'ly where 

 thalamic re-ion ; II-X, cranial nerves ; Sp', first 



spinal nerves. the cerebellum IS extra- 



ordinarily developed), so that it is chiefly the floor of the cavity 

 which is thickened in these parts. On the other hand it is the 

 roof which is thickened to form the optic lobes and the cere- 

 bellum. 



36. The various regions of the brain or encephalon have received the 

 above names as they appear to be comparable to similiarly named 

 regions in higher forms ; but the regions and ventricles are also named, by 

 comparative anatomists, rliiii-,pros-,tlialam-,mes-,ep- and met- encephalon 

 and the ventricles rhinocoele, prosoccele, thalamocoele, mesoccele, epicoe]e, 

 metacoele. Of these ventricles the thalamoctt'le is the most corapHcated 

 as it projects above into the epiphysis, and below into the inferior 

 lobes anil hypophysis. The hypojihysis and epiphysis are not formed of 

 nervous matter like the rest of the brain, for the former is glandular 

 in its nature, while the latter is supposed to be the rudiment of an un- 

 paired eye. 



