194 



SUB-CLASS (AND ORDER) TELEOSTEI. 



(2) The cerebrum is not clearly marked off from the thalamen- 

 cephalon, and its roof is entirely composed of a thin 'pallium. 

 The latero-ventral parts are thickened into the great corpora 

 striata, which were formerly taken for the cerebral hemispheres 

 themselves. The ventricle of the cerebrum is entirely un- 

 divided, and the pallium or dorsal wall of it is not marked by a 

 groove (Fig. 114). 



(3) The thalamencephalon is very inconspicuous and the optic 

 thalami are hardly if at all developed. The anterior part of the 

 thin roof is folded inwards in the usual way (Fig. 113 pj.). The 

 pineal body lies in the skull over the pallium ; it has folded walls 

 and appears to open by a narrow pore at its point of attachment 

 to the roof just in front of the posterior commissure. There is 



no parietal organ. The floor 

 presents the usual structure ; 

 in front is the thickening caused 

 by the optic nerves, which sim- 

 ply cross after leaving the brain 

 and do not form a chiasma. 

 The infundibulum possesses 

 lateral lobi inferiores, and is 

 provided posteriorly with a 

 glandular sac, the saccus vas- 

 culosus, opening into it by a 

 minute pore. The pituitary 

 body is solid and is attached 

 to the infundibulum in front 

 of the saccus vasculosus. 



(4) The mid-brain presents the two optic lobes (corpora 

 bigemina) dorsally and contains a projection formed by the 

 wall of the brain at the junction of the optic lobes and cerebellum. 

 This is the valvula cerebeUi {Vc), or fornix of Gottsche. 



(5) The hind-brain is in the usual form, the cerebellum being 

 large and containing a prolongation of the fourth ventricle. It 

 projects back over the medulla oblongata. In some Teleosteans 

 (e.g. Gymnarchus, llortnyridae) the brain attains a very large 

 size, the cerebellum and sometimes the optic lobes being 

 especially well developed. 



The spinal cord frequently ends in an oval or spherical swell- 

 ing. In some forms [Plectognathi) it is much reduced in length ; 



FlO." 114. — Transverse section through the 

 cerebrum of the trout, through the line 

 XX in Fig. 113. Vcm and Vt Ventricle of 

 the cerebrum ; Cst corpus striatum ; Sm 

 pallium ; Gp pineal body ; PI choroid 

 plexus (after Rabl-Riickhard from 

 Gegenbaiu). 



