BRAIN. . 155 
vasculosus and inferior lobes. On its roofisa large pinealis which reaches the skull in 
afew ganoids. The parietal organ appears in the embryo and soon degenerates; the 
paraphysis is usually well developed. The optic lobes are large and are usually 
divided into two hemispheres by a median groove, but this occasionally is scarcely 
noticeable. The cerebellum is large, much larger than appears from the surface, 
since a considerable part, the valvula, projects into the ventricle of the mid-brain. 
In the cerebellar region there is sometimes an enormous development of the lobes 
of the vagus (fig. 155). 
The brain of Polypterus differs from that of other ganoids in several respects. 
There is no differentiation of cerebral hemispheres; the optic lobes and the cerebel- 
lum are moderate, the latter being thin in the median line and the valvula smaller. 
The medulla oblongata has thin walls and the ventricle is large. The brain has a 
primitive appearance, but it shows little resemblance to those of the amphibia or 
of the dipnoi. 
DIPNOI.—The brains of Lepidosiren and Protopierus differ considerably from 
that of Ceratodus. In all the cerebrum is larger than the optic lobes and the 
Gr 
Fic. 157.—Brain of Protopterus, after Burckhardt. cb, cerebellum; e, epiphysial 
structures; h, hypophysis; z, infundibulum; m, mid brain; se, saccus endolymphaticus; s?, 
spinal nerves; ¢, cerebrum; 1-12, cranial nerves. 
olfactory bulb is separated from the cerebrum by a long olfactory tract. In Cer- 
atodus the hemispheres are united above by a part of the chorioid plexus, while 
internally they are separated from the diencephalon by a well marked velum. The 
pinealis is long and rests upon a large ‘zirbelpolster’ developed as an outgrowth 
of the roof of the third ventricle in front of the superior commissure. The optic 
lobes are separated into two hemispheres, while the cerebellum is scarcely more than 
a transverse plate and is, together with the fossa rhomboidea, covered with a com- 
plicated chorioid plexus. In Protopterus (fig. 157) the elongate hemispheres are 
parallel, the pinealis and its ‘polster’ are smaller and the mid-brain has but a 
single rounded lobe. 
AMPHIBIA.—The parts of the amphibian brain are more distinct from each 
other than is usual in vertebrates, and, except in the gymnophiones, the flexures 
have largely disappeared in the adult. There is a deep intercerebral fissure 
between the hemispheres, but in the anura the two halves of the cerebrum are 
connected by a transverse band just behind the olfactory lobes. The telencephalon 
is relatively larger than in fishes, the increase being due to the invasion of the pal- 
lium by nervous matter, while the corpora striata are relatively smaller than in other 
ichthyopsida. In the pallium the inner part is largely composed of nerve cells, 
the outer layer consisting of nerve fibres. 
The diencephalon, broad in the anura, narrower in the urodeles and czcilians, 
