BRAIN 



213 



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. 



N.ol 



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, H.ol, olfactory lobe and nerve ; Ca, anterior commissure ; 

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

 missure"; Op, posterior commissure; C.st, corpus striatum, which lies on 

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

 of the ventricles ; Gp, pineal body, with a cavity (Gp l ) in its interior ; H, 7/ 1 , 

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

 Tro, roof of the optic lobes ; Tl, torus longitudinalis ; tr, pathetic nerve ; Val, 

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

 (teloccele) ; 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 



