PINEAL GLAND. 
1179 
corpora quadrigemina, and thus become a part of the 
enrolling stations for the nervous action which pro- 
ceeds, according to Luys, between the surface-layers 
of the cerebral hemispheres and the central gray matter 
of the spinal column, i. e. between the psycho- intel- 
lectual and the vegetative life. The ’tweenbrain, on 
the other hand, has developed into the optic thalami, 
which now, hoAvever, have a far greater importance 
than that of mere collectors of the visual sensations, 
for hither, according to Luys (tig. 348), stream all 
the sensations not yet idealised, but destined to the 
consciousness. Here Luys distinguished between four 
centres, well-detined gangliar masses in each optic 
thalamus ( 1 ), the foremost of which receives and trans- 
mits the impulses of smell {20), the second those of 
sight {13 — 14), the third those of touch {8 — 9), the 
fourth those of hearing {3 — 4). Before and outside 
the optic thalami lies the primitive floor of the cerebrum 
was a time when it was supposed that the soul had a 
fixed and special station in some part of the brain, and 
Descaiites assumed that the pineal gland was the seat 
of the soul: — it had such a remarkably central situa- 
tion, and it was solitary, unpaired. Had the soul dwelt 
in a paired organ, said Descartes, we should always 
have two ideas about the same thing, and there would 
be a continual conflict to determine which side should 
have the mastery. The researches of modern times 
have certainly divested the pineal body of most of its 
reputation from this point of view; but its historical 
importance claims all the greater recognition. 
Before the transformation of the ’tweenbrain into 
optic thalami, even before the appearance of the rudi- 
ment of the true optic thalami, this part of the brain 
grows laterally outwards in a vesicular form and sup- 
plies the rudiments of the eyes and optic nerves, and 
in a downward direction it forms an expansion known 
c stp Ibrs Id A Id 
sip c r 
Fig. 349. Ripe female of the Lampern ( Petromyzon fluviatilis, forma branchialis ), nat. size. A, from the left; B, forepart, from above; C , the 
same, from below. 
c, anterior connecting branch between the frontorostral canals; stp, posterior connecting branch; r, rostral branch; so, suborbital branch; 
m, mandibular branch; Im , mediolateral line; Id, dorsolateral line; Ibrs, superior brancbiolateral line; Ibri, inferior branchiolateral line. 
(forebrain), the so-called corpora striata {2), to which 
the manifestations of consciousness that have been de- 
rived from the said sources and developed in the sur- 
face-layers of the cerebral hemispheres are conducted 
{14— 15— 16— 17 ; 9—10—11—12 and 4—5—6) for 
their first realisation, with that contribution to the 
power and distinctness of the currents which is supplied 
by the little brain, whose upper peduncles, according 
to Luys, by means of their yellow fibrils join the gang- 
lion cells in the yelloAV nucleus of each corpus striatum. 
BetAveen the optic thalami and the corpora quadrigemina 
lies a small SAvelling, the pineal gland {Ep in tig. 347), 
the history of Avhose transformations is among the most 
remarkable. In man the nervous matter of the pineal 
body probably plays the same part as that of the cor- 
pora quadrigemina, but is of less importance. Yet there 
as the underbrain {Inf. in fig. 346); but in the roof of 
the ’tweenbrain there appear two thickenings of the 
cerebral Avail (behind Ep in fig. 347), situated side by 
side and usually of unequal size. These collections of 
nervous matter become the rudiments of the true optic 
thalami. Over the ’tweenbrain the cerebral wall has 
grown out into a vesicular SAvelling {Ep in figs. 346, 
347), which is at first flattened, but rises, becomes tu- 
biform, and grows fonvard over the brain. This is the 
first appearance of the pineal gland in the loAver verteb- 
rates, and in them it attains a considerable develop- 
ment. In the Lampreys it is even externally visible 
through the skin as a light, round spot behind the 
tubular aperture of the nostril (fig. 349, B). 
The pineal gland belongs, as mentioned above, to 
that division of the brain with Avhich the origin of the 
