374 



FISHES 



\-rh 



-partZ' 



pros 



melac- 



inner ones extend into the hemispheres as lateral ventricles, 

 and the two outer as rhinocoeles into the olfactory lobes (Fig. 

 214). In connexion with the infundibulum there is a pair of 

 sacci vasculosi, consisting mainly of gland-tubules, opening into 

 the infundibular cavity.^ The cerebellum is exceptionally large, 



but it does not form a " valvula cere- 

 belli." Large ear-like corpora resti- 

 formia are present. The third and 

 fourth ventricles alone retain an epi- 

 thelial roof in relation with choroid 

 plexuses. 



In all essentials the brain of the 

 Holocephali is a repetition of the 

 Elasmobranch type, more especially of 

 the elongated form seen in Noticlamis. 

 Indications of a higher grade of struc- 

 ture are, however, to be seen in the 

 reduction of the prosencephalon which, 

 with its prosocoele, is now scarcely 

 distinguishable from the thalamen- 

 F.G. 214. -Horizontal longitu- ccphalon and its Ventricle ; and in the 

 dinai section of brain of CAiZo- more Complete differentiation of the 



scyllinm, to show the veiitri- i i u • i j^ j.i 



cles ; semi-diagrammatic, cer, cerebral hemispheres from one another 

 Origin of cerebellar ventricle and from the rest of the brain. Large 



or epicoele ; diet, third ven- n -t, ^ , ■ ,. . 



trilled corpora restiiormia are con- 

 spicuous structures on each side of the 

 medulla oblongata. Besides the usual 

 intra-cranial pituitary body, there is 

 also a separate extra-cranial portion 

 lodged in a pit on the ventral surface of the basis cranii : in the 

 embryo the two are continuous. 



In the Teleostomi the brain is distinctly of a more primitive 

 type than in any other Fishes (Fig. 215).^ The most striking 

 feature is the absence of cerebral hemispheres, the evolution of 

 the primary fore-brain proceeding no farther than the formation 

 of an undivided prosencephalon with a non-nervous roof, and 

 a prosocoele which forms a continuous cavity with the third 

 ventricle, or at the most is only separated from it by an infolding 



' The sacci probably secrete the fluid contents of tlie ventricles. 

 ■■^ Haller, Morph. Jalvrl. xxvi. 1898, p. 34.5. 



tricle ; iter, mesocoele ; ■nieta, 

 fourth ventricle ; opt, opto- 

 coele, or cavity of an optic 

 lobe ; para, lateral ventricles ; 

 pros, prosocoele ; W?,rhinocoele. 

 (From Parker and Haswell.) 



