Section is cut about 1.5 cm. to the right of the median plane. _M_,
Medulla oblongata; _P_, pons; _P.c._ (above _M_), chorioid plexus of
fourth ventricle; _C.m._, central white matter (corpus medullare) of
cerebellum and of cerebrum; _P.c._ (in front of _P_), cerebral
peduncle; _H_, hippocampus; _V_, lateral ventricle; _T_, thalamus;
_N.c._, caudate nucleus; _C.i._, internal capsule; _N.l._,
lenticular nucleus; _B.o._, olfactory bulb.
]
The =corpus striatum=[202] is the great basal ganglion of the
hemisphere. It is situated in front of the thalamus and the cerebral
peduncle, and its anterior rounded end appears on the base of the
hemisphere at the trigonum olfactorium. It is composed of two masses of
gray matter, the caudate and lenticular nuclei, separated incompletely
by tracts of white matter which are known collectively as the internal
capsule. The =caudate nucleus= (Nucleus caudatus) is the dorso-medial
and larger of the two gray masses; it has been seen in the examination
of the floor of the lateral ventricle. The =lenticular nucleus= (Nucleus
lentiformis) lies ventro-laterally, over the trigonum olfactorium and
the fossa transversa. It is related externally to a layer of white
matter termed the =external capsule=, which separates it from a stratum
of gray substance known as the =claustrum=. The two nuclei are fused in
front, and further back they are connected by strands of gray matter
which intersect the internal capsule.
The =amygdaloid nucleus= (Nucleus amygdalæ) (Fig. 506) is an ovoid mass
of gray matter situated external to the ventral horn of the lateral
ventricle and below the posterior part of the lenticular nucleus. Some
fibers of the stria terminalis are connected with it.
The =internal capsule= (Capsula interna) is a broad band of white matter
situated between the thalamus and caudate nucleus internally and the
lenticular nucleus externally. A sagittal section through the brain
shows that it is in great part directly continuous with the basis or
ventral part of the cerebral peduncle. It contains most of the so-called
=projection fibers= of the hemisphere, which connect the cerebral cortex
with nuclei of other and more posterior parts of the brain. When the
fibers of the internal capsule are traced forward it is evident that
they spread out in all directions to reach the cerebral cortex. This
arrangement, in which the fibers of the corpus callosum participate, is
termed the =corona radiata=.
The internal capsule also contains fibers which connect the corpus
striatum with the thalamus. These are termed the thalamo-striate and
strio-thalamic fibers respectively, according to the direction in
which they conduct impulses.
The fibers of the stria terminalis connect the amygdaloid nucleus with
the septum pellucidum and trigonum olfactorium. It is therefore
probably part of the complex connections between the primary and
secondary olfactory centers.