504 THE NERVOUS SYSTEM. 
has important connexions with the optic tract. The corticipetal tegmental tracts, 
which enter it from below, will be noticed in connexion with the subthalamic 
region. Suffice it to say, for the present, that many of these fibres end in the midst 
of the thalamus in connexion with the thalamic cells, whilst others are apparently 
carried directly upwards through it to enter the internal capsule; the latter with- 
out any break in their continuity, reach the cortex of the cerebrum. In addition 
to these, enormous numbers of fibres, arising within the thalamus as the axons of its 
cells, stream out from its outer and under surfaces to form the thalamic radiation. 
These fibres pass to every part of the cortex ; and although there is no separation of 
them into distinct groups as they leave the thalamus, it is customary to regard 
them as constituting a frontal stalk, a parietal stalk, an occipital stalk, and a 
ventral stalk. 
The frontal stalk of the thalamic radiation emerges from the anterior part of the lateral 
surface of the thalamus and passes through the anterior limb of the internal capsule, to reach the 
cortex of the frontal lobe. Many of these fibres end in the caudate and lenticular nuclei, between 
which they proceed. The parietal stalk issues from the lateral surface of the thalamus, and, 
passing through the internal capsule (and to some extent, also, through the lenticular nucleus 
and the external capsule), gains the cortex of the hinder part of the frontal lobe and of the 
parietal lobe. The occipital stalk emerges from the outer aspect of the pulvinar and constitutes 
the so-called optie radiation. These fibres 
“sweep outwards and backwards round the 
outer side of the posterior horn of the 
lateral ventricle to gain the cortex of the 
occipital lobe. The ventral stalk streams 
out from the under aspect of the anterior 
part of the thalamus, in front of the sub- 
AST er thalamic tegmental region and the corpus 
mamumillare. Its fibres arise in both the 
mesial and lateral nuclei, and sweep down- 
wards and outwards to reach the region 
_|--ANT® LIMB 2 : E * a 
Monee below the lenticular nucleus. One very 
distinct band which lies dorsal to the 
other fibres (ansa lenticularis) enters the 
lenticular nucleus, whilst the remainder 
B-Post® Lime (ansa peduncularis) continue in an outward 
IKI direction below the lenticular nucleus and 
gain the cortex of the temporal lobe and of 
the insula or island of Reil. 
CORP:GEN: INT Flechsig divides the thalamo-cortical 
' sup quaptsopy fibres of ordinary sensation into three 
a sensory systems. These he has been able to 
) 0 distinguish by studying the order in which 
they assume their sheaths of myelin in the 
.MESNCEPHALON foetus and infant. 
ae Ferrier and Turner, by the degenera- 
tive method of investigation, corroborate 
Flechsig’s results in a very remarkable 
manner. They confirm the observation of 
Lys eee ata Flechsig that, while thalamic fibres are dis- 
sRIAGA: tributed to the several regions of the cere- 
bral cortex to an almost equal extent, there is 
one district, viz. the frontal pole, to which 
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LOBE the supply is scanty. Another very im- 
Fia, 374.—ScHeMa. Founded on the observations of ed ae pee ee Ce by be 
Flechsig, and Ferrier and Turner. authors. ley have established the fac 
that many of the thalamic fibres cross the 
mesial plane in the corpus callosum, and thus gain the cortex of the opposite cerebral hemisphere. 
Hamilton’s crossed callosal tract thus receives confirmation. 
Intimate Structure of the Corpus Geniculatum Externum.—Sections through the 
external geniculate body reveal the fact that it is composed of a series of alternately 
placed gray and white curved laminew. This gives it a very characteristic appear- 
ance. The white lamine are composed of fibres which enter the body from the 
optic tract and the optic radiation. The connexions of the geniculate bodies will 
be studied with the optic tract. 
Subthalamic Tegmental Region.—The tegmental part of the crus cerebri is 
prolonged upwards and assumes a position below the hinder part of the thalamus. 
