ular Nucleus.]

The _pineal body_ is a reddish cone-shaped body situated upon the
anterior pair of the corpora quadrigemina (see figs. 3 and 6). From
its broad anterior end two white bands, the _peduncles_ of the _pineal
body_, pass forward, one on the inner side of each optic thalamus.
Each peduncle joins, along with the taenia semicircularis, the
anterior pillar of the fornix of its own side. In its structure this
body consists of tubular gland tissue containing gritty calcareous
particles, constituting the _brain sand_. Its morphology will be
referred to later.

A general idea of the internal structure of the brain is best obtained
by studying a horizontal section made just below the level of the
Sylvian point and just above the great transverse fissure (see fig.
14). Such a section will cut the corpus callosum anteriorly at the
genu and posteriorly at the splenium, but the body is above the plane
of section. Behind the genu the fifth ventricle is cut, and behind
that the two pillars of the fornix which here form the anterior
boundary of the third ventricle. At the posterior end of this is the
pineal body, which the section has just escaped. To the outer side of
the fornix is seen the foramen of Munro, leading into the front of the
body and anterior horn of the lateral ventricle. It will be seen that
the lateral boundary of this horn is the cut caudate nucleus of the
corpus striatum, while the lateral boundary of the third ventricle is
the cut optic thalamus, both of which bodies have been already
described, but external to these is a third triangular grey mass, with
its apex directed inward, which cannot be seen except in a section.
This is the lenticular nucleus of the corpus striatum, the inner or
apical half of which is of a light colour and is called the _globus
pallidus_, while the basal half is reader and is known as the
_putamen._ External to the putamen is a long narrow strip of grey
matter called the _claustrum_, which is sometimes regarded as a third
nucleus of the corpus striatum. These masses of grey matter, taken
together, are the basal nuclei of the brain. Internal to the
lenticular nucleus, and between it and the caudate nucleus in front
and the thalamus behind, is the _internal capsule_, through which run
most of the fibres connecting the cerebral cortex with the crus
cerebri. The capsule adapts itself to the contour of the lent