BRAIN 



213 



b^^ 



part of the telencephalon consists of large paired basal ganglia 

 (corpora striata) connected together by an anterior commissure 

 The olfactory lobes are either closely applied to the telencephalon 

 and contain a small ventricle, or they become differentiated into 

 olfactory tract and bulb, as in Elasmobranchs. 



FIG. 161. LONGITUDINAL VERTICAL SECTION THROUGH THE ANTERIOR PART OF 

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

 Riickhard.) 



Aq, iter (mesoccele); B.ol, N.of, olfactory lobe and nerve ; Ca, anterior commissure ; 

 Ch, posterior optic; Ch.n.opt, optic chiasma ; Ci, "inferior com- 

 missure"; Op, posterior commissure; O.st, corpus striatum, whicli lies on 

 either side of the middle line ; E)>, the epithelium (ependyme), lining the walls 

 of the ventricles ; Gp, pineal body, with a cavity (Gj) 1 ) in its interior ; ff, //', 

 hypophysis ; J, infundibulum ; Li, lobi inferiores ; Sv, saccus vasculosus ; 

 TVo, roof of the optic lobes ; Tl, torus longitudinalis ; fr, pathetic nerve ; Val, 

 valvula cerebelli ; V.cm, common ventricle of the secondary fore-brain 

 (teloctele) ; V.t, third ventricle ; t, point at which the epithelial roof of the 

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

 anterior wall of the pineal tube ; above /is seen an outgrowth which represents 

 a rudimentary parietal organ. 



The diencephalon is very small, and is depressed between the 

 telencephalon and mid-brain. The epiphysis (Figs. 160, 161) is 

 plainly distinguishable, but it usually does not pass into the roof 

 of the skull ; an outgrowth arising from the roof of the brain in 

 front of the epiphysis represents the parietal organ, but this 



