540 THE NERVOUS SYSTEM. 
The external capsule is loosely connected with the outer surface of the putamen, and it can be 
readily stripped off. This accounts for the tendency, exhibited in hemorrhages in this locality, 
for the effused blood to spread out in the interval between these structures. 
The globus pallidus is composed of the two smaller and inner zones of the lenti- 
cular nucleus. They present a faint yellowish tint, and are paler and more 
abundantly traversed by fibres than the putamen. ‘The zone next the putamen (@.e. 
the intermediate zone) is much larger than the innermost subdivision. It extends 
forwards to a point a little in front of the plane of the anterior commissure. When 
the lenticular nucleus is cut in a coronal direction, and in its widest part, the 
innermost zone shows an indication of a separation into two parts, so that here the 
globus pallidus appears to consist of three subdivisions. The morphology of the 
globus pallidus is by no means clear. 
Connexions of the Corpus Striatum.—(1) Numerous fibres from the optic 
thalamus pass into the anterior limb of the internal capsule and enter both the caudate 
and the lenticular nuclei. ‘These may be termed the thalamo-striate fibres. (2) Edinger 
Intersection of corona radiata 
and callosal systems of fibres 
Fornix—e) \ = im es Claustrum 
g 
Frontoparietal operculum 
Insula 
Temporal operculum 
Fie, 403.—CoronaL SECTION THROUGH THE LEFT SIDE OF THE CEREBRUM OF AN ORANG 
(Weigert- Pal specimen). 
The section passes through the middle of the lenticular nucleus. 
describes a connexion between the caudate nucleus and the substantia nigra. The con- 
necting fibres pass through the subthalamic region and constitute a tract in the mesen- 
cephalon, in close apposition with the substantia nigra, called the stratum intermedium. 
(3) The ansa lenticularis has previously been described. It is composed of fibres which 
come from the inferior part of the fore portion of the thalamus and curve outwards under 
the lenticular nucleus. They stream upwards into this and through its medullary 
laminee. Many of them apparently proceed onwards to the cerebral cortex. (4) Fibres 
from the posterior limb of the internal capsule (thalamic fibres chiefly) enter the lenticular 
nucleus and stream through it, and its medullary laminz, on their way to the cerebral 
cortex. 
Claustrum.—This is a thin plate of gray substance embedded in the white 
matter, which intervenes between the lenticular nucleus and the gray cortex of the 
