538 THE NERVOUS SYSTEM. 
horizontal section, it presents a shape similar to that of a biconvex lens. Its 
inner surface bulges more than the outer surface, and its point of highest convexity 
is placed opposite 
the tenia semi- 
circularis or the in- 
terval between the 
caudate nucleus 
and the optic 
thalamus. In 
coronal section the 
appearance pre- 
sented by the len- 
ticular nucleus 
Claustran liffers very much 
in different planes 
es of section. Fig. 
Putamen 401 represents a 
section through its 
anterior portion. 
Here it is semi- 
lunar or crescentic 
in outline and is 
cirectly continuous 
Tail of below with the head 
cane Uvof thetrcamdane 
Optic nucleus; above, 
radiation algo, it 18 inti- 
Tapetum mately connected 
Inferior - 
longitudinal With the caudate 
po nucleus by bands 
of gray matter, 
which pass be- 
tween the two 
nuclei and break 
up the white 
matter of the fore- 
part of the inter- 
vening internal 
capsule. It is due 
to the ribbed or 
barred appearance, 
which is presented 
by such a section 
as this, that the term corpus striatum is applied to the two nuclei. In the region 
of the locus perforatus anticus both nuclei reach the surface and become continuous 
with the cortex. 
When a section is made in a plane further back (e.g. immediately posterior to 
the anterior commissure, as in Fig. 402) the divided lenticular nucleus assumes an 
altogether different shape, and is seen to be completely cut off from the caudate 
nucleus by the internal capsule. It is now triangular or wedge-shaped. Its base 
is turned towards the island of Reil and is in direct relation to a thin lamina of 
white matter, termed the external capsule. Its internal surface is oblique and is 
applied to the internal capsule, whilst its inferior surface is horizontal and is 
directed downwards towards the base of the brain. But, further, two white lamine, 
the external and internal medullary lamine, are now evident, which traverse its 
substance in a vertical direction and divide it into three zones. The outer, basal, 
and larger zone is termed the putamen ; the two inner portions together constitute 
the globus pallidus. 
The putamen forms much the largest part of the lenticular nucleus. It ig * 
al 
Genu of corpus callosum—— 
Anterior horn of lateral | ae 
ventricle 
Caudate nucleus———— 
| 
| 
Anterior limb of internal 
capsule | 
Ventricle V. 
Genu of internal capsule 
7 
Anterior pillars of fornix-49)%) 
Globus pallidus 
Bundle of Vieq a’ Azyr—ees 
Posterior limb of internal 
capsule | 
Thalamus—— 
Retrolenticular part of WwW 
internal capsule i\s 
ea ae 
Hippocampus major—- 
Splenium 
Choroid plexus 
Band of Vieq ad’ Azyr 
Calearine fissure— 
Fie. 400.—HorizonraL SECTION THROUGH THE RIGHT CEREBRAL HEMISPHERE 
AT THE LEVEL OF THE WIDEST PART OF THE LENTICULAR NUCLEUS. 
