140 



COMPARATIVE ANATOMY. 



remains in an embryonic condition, and can hardly be said to have a 

 physiological function ; the brain of those Fishes in which this con- 

 dition is retained probably acts mainly as a reflex machine, 

 and there is little doubt that the mental processes 



N.ol 



Fici 113A. LONGITUDINAL VERTICAL SECTION THROUGH THE ANTERIOR PAIIT <>! 

 THE TELEOSTEAN BRAIN. (Founded on a figure of the Trout's brain by Rabl- 

 Kiickhard.) 



Tco, roof of the optic lobes ; 77, torus longitndinalis ; Op, posterior commissure ; 

 Gp, pineal gland, with a cavity (Gp 1 ) in its interior ; Ep, Ep, the ppendyma, 

 which lines the walls of the ventricles ; t, point at which the epithelial roof of 

 the secondary fore-brain (pallium. Pa) becomes continuous with the lining of the 

 {interior wall of the pineal tube: the former is folded inwards at /; V.cm, 

 common ventricle of the secondary fore-brain ; V.t, third ventricle ; B.ol, N.ol, 

 olfactory bulb and nerve ; C.st, corpus striatum, which was formerly taken to 

 represent the whole of the prosencephalon, and which lies on either side of the 

 middle line; Ch.n.opt, optic chiasma ; Ci, inferior commissure (Gadden) ; Ch, 

 horizontal commissure (Fritsch) ; /, infundibulum ; IT, 7/ 1 , hypophysis ; ,SY, 

 saccus vasculosus ; Li, lobi inferiores ; Aq, aqueduct of Sylvius ; It; trochlear 

 nerve ; I'al, valvula cerebelli. 



which take place in the cortical gray substance of the 

 brains of higher Vertebrates do not obtain in them. 



The mid-brain and cerebellum are by far the largest 

 portions of the brain (Figs. 114 and 115, MIf, ////), while the 

 thalamencephalon is depressed between the prosencephalon and 



