1178 
SCANDINAVIAN FISHES. 
When Ahlborn resumed the study of the brain of 
the Lampreys in 1883“, its structure appeared in a new 
light, different from that shed upon it in Joh. Muller’s 
day. In the brain of the lower vertebrates (fig. 347) 
a distinction is now drawn in the first place between a 
posterior and an anterior part. The posterior, epichor- 
dal part — so called because it extends as far forward 
as the subjacent chorda dorsalis — contains the medulla 
oblongata (prolongated spinal cord or afterbrain, Mob) 
and the small homologue of our little brain (hindbrain 
or cerebellum, Cbl), but in the Lampreys is almost as 
15 6 10 
Fig. 348. Diagram of a longitudinal section through the human ce- 
rebrum and medulla oblongata, to illustrate the higher functions of the 
brain, according to the assumptions advanced by Luys. 
7, thalami optici; 2 , corpora striata; 3, course of the propagation of 
acoustic impressions (labyrinth of the internal ear). These impressions 
arrive in the corresponding centre (4), are radiated towards the sen- 
soriurn (3), and reflected at 6 , to the large cells of the corpus striatum, 
and thence at 7 and 7', towards the motor regions of the spinal axis. 
8. Course of sensitive impressions. These are concentrated (at 9) in 
the corresponding centre, radiated thence into the plexuses of the sen- 
sorium (10), reflected to the large cortical cells (11), and thence pro- 
pagated to the large cells of the corpus striatum, and finally to the 
different segments of the spinal axis. 13. Course of optic impressions. 
These are concentrated (at 14) in their corresponding centre, then 
radiated towards the sensorium (at 15). They are reflected towards the 
large cells of the corpus striatum and afterwards propagated to the 
different segments of the spinal axis; 18, 19', 19", the antero-lateral 
fibres from their point of origin in the corpus striatum, are invested by 
the elements of cerebellar innervation which begin to appear in the 
peduncles (19), to become considerably thicker at 19' , on a level with 
the region called the pons, and to diminish insensibly on a level with 
the medullary regions, 19" . — 20, peripheral expansion of the ol- 
factory nerves. 
large as the whole anterior portion, the so-called pre- 
chordal part. All the cranial nerves, except those of 
sight and smell, have their roots in this posterior part 
of the brain. In the prechordal brain the homologue 
of the brain proper (forebrain or cerebrum, Cb) of the 
higher animals is merely a small, hollow prominence 
on each of the two olfactory lobes (. L . old). The two 
parts of the brain which are incomparably most deve- 
loped in man — the cerebrum and cerebellum — are thus 
the smallest in the Lamprey; and but little, though 
somewhat, greater is the development of the cerebrum 
in true fishes (Teleosts) and batrachians. Merely for 
anatomical reasons it has been possible to prognosticate 
that in these animals the cerebrum is simply a gathering- 
place and a control-station for the sensations coming 
from the organs of smell. In 1868 Goltz successfully 
extirpated the cerebrum of frogs, which still lived for 
some time ‘‘with their intelligence preserved,” as he 
expressed it; and in 1886 the same experiment was 
performed on fishes by Steiner at Heidelberg and Vul- 
pian in Paris. A Carp which lived six months after 
the removal of its cerebrum (forebrain), the other parts 
of the brain, even the olfactory lobes, being left intact, 
showed no other irregularity of behaviour, according to 
Vulpian, after the wound had healed, than that it was 
apparently destitute of the sense of smell. Yet in the 
higher vertebrates that part of the brain of which it 
was deprived, is the foundation for the subsequent de- 
velopment of the material substratum in everything that 
bears the name of consciousness. Thus in the fish it 
is only those ganglion cells with which the conscious 
apprehension of the impulses of smell is bound up that 
lie there. Another part of the prechordal brain appears 
in fishes to occupy exactly the same relations to the 
stimuli of sight. This is the postero-superior part, 
the so-called midbrain (ME), which on the dorsal side 
is closely applied to or even confluent with their little 
brain. The first control-stations for the sensations of 
sight within the region of the brain, however, lie in 
the antero-inferior part of the median portion of the 
prechordal brain, the so-called ’tweenbrain (fig. 347, 
Till). Originally, as here in the Lampreys, the ’tween- 
brain and midbrain enclose that cavity of the brain 
known as the third ventricle, and this they also do in 
the embryos of the highest vertebrates; but in the adult 
brain of the latter they have sunk down to the bottom 
of the ventricle; and before this has happened, great 
revolutions have taken place in the surroundings of 
that ventricle. The midbrain has dwindled into the 
Unclers. tib. das Gehirn der Petromyzonten, Zeitschr. f. Wiss. Zool., Bd. 39. 
