1178 



SCAXDINAVIAX PISHES. 



When Ahlbokn resuiued tlie 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 tlic first place between a 

 posterior and an anterior part. Tlie posterior, epichor- 

 dal part — so called because it extends as far forward 

 as the subjacent chorda dnrsalis — contains the medidla 

 oblongata (prolongated sj)inal cord or afterbrain. Mob) 

 and the small homologue of our little brain (hindbrain 

 or cerebellum, Cbl), but in the Lampreys is almost as 



Fig. .'548. Diagram of a longitudinal section through the human ce- 

 rel>ruiii and medulla oblongata, to illustrate the higher functions of the 



brain, according to the assumptions advanced by LuYS. 

 /, 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- 

 soriura (i5), 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 a.xis. 13. Course of optic impressions. 

 These are concentrated (.it 14) in tlieir corresponding centre, then 

 radiated towards the sensorium (at 10). Tiicy 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 

 pedimcles (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 anterioi' portion, the so-called pre- 

 chordal part. All the cranial nerves, except those of 



" Unders. lib. das Gehirn der Peiromyzonten, Zeitschr. f. Wiss, 



sight and smell, have tlieir r<jots in this posterior part 

 of the Vjrain. In the prechord;d lirain 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. oh). 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 

 extii-pated the cerebrum of frogs, wiiich still lived for 

 some time "with their intelligence preserved," as he 

 expressed it; and in 1886 the same experiment was 

 performed on fishes by Steixer at Heidelljerg and VuL- 

 PIAN in Paris. A Carp which lived si.x 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 l)rain appears 

 in fishes to occupy exactly the same relations to the 

 stimuli of .sight. This is the postero-superior part, 

 the so-called midbi'ain {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 antcro-inferior part of the median portion of tlie 

 prechordal brain, the so-called 'tweenbrain (fig. 347, 

 TM). Originally, as here in the Lamprej's, the 'tween- 

 brain and midlirain 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 hapj^ened, great 

 revolutions have taken place in the surroundings of 

 that ventricle. The midlirain has dwindled into the 

 Zool., Bd. .39. 



