374 FISHES CHAP. 
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 
saccl 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 Wotidanus. 
Indications of a higher grade of strue- 
ture are, however, to be seen in the 
reduction of the prosencephalon which, 
with its prosocoele, is now scarcely 
distinguishable from the thalamen- 
cephalon and its ventricle; and in the 
Fic. 214.—Horizontal longitu- < maa 
dinal section of brain of Chilo- more complete differentiation of the 
scyllium, to show the ventri- __, j acd P P > 
eles + semi diserammatic. teen cerebral hemispheres from one another 
Origin of cerebellar ventricle and from the rest of the brain. Large 
or epicoele ; dia, third ven- felled wegrcon contifrannin . 
tricle ; iter, mesocoele; meta, {tilled corpora restiformia are con- 
fourth ventricle ; opt, opto- spicuous structures on each side of the 
coele, or cavity of an optic ; =e 
lobe ; para, lateral ventricles; Medulla oblongata. Besides the usual 
pros. prosocoele; rh,rhinocoele. intra-cranial pituitary. body, there is 
(From Parker and Haswell.) 2 ; 
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).2 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 
1 The sacci probably secrete the fluid contents of the ventricles. 
* Haller, Morph. Jahrb. xxvi. 1898, p. 345. 
