164 



COMPARATIVE ANATOMY 



The mid-brain (Fig. 133) is extremely large relatively, while 

 the thalamencephalon is depressed between it and the prosen- 

 cephalon. 



The extremely well-developed cerebellum is bent upon itself, 



i 



FIG. 134. LONGITUDINAL VERTICAL SECTION THROUGH THE ANTERIOR PART OF 

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

 Riickhard. ) 



Tco, roof of the optic lobes ; Tf, torus longitudinalis ; Cp, posterior commissure ; 

 Gp, pineal body, with a cavity (Gp l ) in its interior ; Ep, Ep, the epithelium 

 (ependyme), lining 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 anterior wall of the pineal tube ; at/ is seen an outgrowth which 

 represents a rudimentary parietal organ ; V.cm, common ventricle (prosocoele) 

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

 and nerve ; C.st, corpus striatum, which lies on either side of the middle 

 line; Ch.n.opt, optic chiasma ; Ci, inferior commissure; Ch, horizontal com- 

 missure ; J, infundibulum ; H, H l , hypophysis ; Sv, saccus vasculosus ; 

 Li, lobi inferiores ; Aq, aqueduct of Sylvius (mesocoele) ; tr, pathetic nerve ; 

 Val, valvula cerebelli. 



overlies the medulla oblongata behind, and is prolonged in front 

 "into the ventricle of the mid-brain as a valvula cerebelli (Fig. 134), 

 as is the case in Ganoids. 



The Teleostean brain is of a specialised type. It has no direct 



