190 THOMPSON YATES LABORATORIES REPORT 
position opposed to gravity. Since they never run into obstacles, the movements of the animal are 
always under some guidance. 
It is probable that we are dealing here with symptoms resulting from the activity of the 
remaining parts of the central nervous system relieved from the control of the cerebral hemispheres. 
2. The function of the strio-thalamic tract is unknown ; it may be noted, however, that of 
the two parts of the surface of the brain which are excitable by the faradic current, one is situated 
on the lateral aspect of the hemisphere, in a position corresponding to the junction of the 
strio-thalamic with tlie common origin of the occipito-mesencephalic and occipito-frontal tracts 
(Figs. 51, 52, 53). We here found that stimulation of this area was followed by rotation of the 
head and neck to the opposite side, and a simultaneous movement of pecking and deglutition ; and 
ScHRADER, from his experiments, came to the conclusion that injury in the thalamus deprived a 
falcon of the power of swallowing — that is, of getting meat placed in its beak into the pharynx. 
Observations and Experiments in Connection with Vision 
The Tractus occipito-mesencephalkus may be regarded as the earliest representative in the 
animal series of the important system of fibres existing in the higher vertebrates which connect 
the primary optic centres — the optic lobes — with the cerebral hemispheres, though it is possible, 
according to Edinger,* that the higher reptiles possess in a much less developed form such a tract. 
In the Bird the occipital lobes are largely developed, and in addition to their connection 
with the optic lobes, are brought into relation with the frontal regions by the associational tracts, 
and with each other by the anterior commissure. 
Our experiments show that the constant result of interference with one hemisphere is 
marked deficiency of vision in the opposite eye. This result occurs after removal of the anterior 
or posterior portion of the cerebral hemisphere, after removing the pallium or destruction of the 
great cell mass of the hemisphere, leaving the pallium intact, thus demonstrating the complicated 
and extended relations of the visual tracts. 
No alteration is seen in the pupils after such operations ; they remain in equal size and 
re-act promptly to light. This observation is also made by Munzer and Wiener. Injury to 
one object vesicle also causes deficiency of vision in the opposite eye. 
Several further questions arise ; MuNKt removed one hemisphere and enucleated the eye 
of the opposite side, and showed that the animals were still able to avoid obstacles, and that they 
thus possessed a visual guidance independent of the hemisphere. The observation has been 
confirmed by Stefani,! Munzer and Wiener,§ and ourselves. This result probably depends on 
the integrity of commissural fibres connecting the two opposite lobes by means of which the eye 
is placed in connection with tlie hemisphere of its own side. Stefani maintains that permanent 
complete blindness results if, when one hemisphere is removed, together with the opposite optic 
lobe, the eye of the same side as the injured hemisphere is enucleated. Munzer and Wiener, 
however, found that blindness did not occur in such cases when a newly-fledged Bird was made 
* Edinger, 3. ' Neue Studien iiber das Vorderhirn der Rcptilien ;' 
' Abhandlungen der Sencken. Naturforsch. Gesell.,' 1896. 
t Mimk, 'Ber. d. k. Preuss. Akad.,' Berlin, 1888. 
I Stefani, ' Phys. Centralb.,' vol. 3, p. 323, 1889 
^ Miinztr ami Wiener, loc, cit. 
