376 FISHES CHAP. 
and the absence of corpora restiformia. This type of brain is 
most strongly marked in the Teleostei, but in other Teleo- 
stomes some, like Acipenser, are typically Teleostean in this 
respect (Fig. 216), while others, such as JLepidosteus, have 
small cerebral hemispheres with lateral ventricles as well as a 
prosencephalon. 
The most obvious feature in the brain of the Dipnoi is the 
great development of the cerebral hemispheres. In this respect 
these Fishes approach the Amphibia, but in other features of brain- 
pn.o. 
Fig. 216.—Vertical longitudinal section of the brain of a Sturgeon (Acipenser ruthenus.) 
c.p, Posterior commissure ; ¢.r, cranial roof ; ic, mesocoele ; op.ch, optic chiasma ; 
p.ch.p, posterior choroid plexus; v.c, valvula cerebelli; v.4, velum transversum ; 
v.ili, v.iv., the third and fourth ventricles ; other lettering as in Fig. 210. (From 
Goronowitsch.) 
structure they present points of agreement with most other 
groups of Fishes without being closely related to any one of them. 
In Protopterus* (Fig. 217) the hemispheres are quite distinct 
except behind, and the walls of their spacious lateral ventricles 
are entirely nervous. Olfactory lobes are sessile on their anterior 
extremities, and behind and below they enlarge into ventral lobes 
which probably represent the hippocampal lobes of the higher 
Vertebrates. A vesicular pineal body at the end of a slender 
stalk overlies a singular conical projection from the roof of the 
thalamencephalon or “pineal pillow.” The optic lobes form a 
single oval body, and, as in Petromyzon and the Amphibia, the 
1 Goronowitsch, Morph. Jahrb. xiii. 1888, p. 427. 
° Burckhardt, Das Central-Nervensystem v. Protopterus annectens, Berlin, 
1892. 
