icular
nucleus and has an anterior limb, a bend or genu, and a posterior
limb. Just behind the genu of the internal capsule is a very important
region, for here the great motor tract from the Rolandic region of the
cortex passes on its way to the crusta and spinal cord. Besides this
there are fibres passing from the cortex to the deep origins of the
facial and hypo-glossal nerves. Behind the motor tracts are the
sensory, including the fillet, the superior cerebellar peduncle and
the inferior quadrigeminal tract, while quite at the back of the
capsule are found the auditory and optic radiations linking up the
higher (cortical) and lower auditory and visual centres. Between the
putamen and the claustrum is the _external capsule_, which is smaller
and of less importance than the internal, while on the lateral side of
the claustrum is the white and then the grey matter of the central
lobe. As the fibres of the internal capsule run up toward the cortex
they decussate with the transverse fibres of the corpus callosum and
spread out to form the _corona radiata._ It has only been possible to
deal with a few of the more important bundles of fibres here, but it
should be mentioned that much of the white matter of the brain is
formed of association fibres which link up different cortical areas,
and which become medullated and functional after birth.

_Weight of the Brain._

This has been the subject of a great deal of research, but the results
are not altogether conclusive; it seems, however, that, although the
male brain is 4 to 5 oz. heavier than that of the female, its relative
weight to that of the body is about the same in the two sexes. An
average male brain weighs about 48 oz. and a female 43-1/2 oz. The
greatest absolute weight is found between twenty-five and thirty-five
years of age in the male and a little later in the female. At birth
the brain weighs comparatively much more than it does later on, its
proportion to the body weight being about 1 to 6. At the tenth year it
is about 1 to 14, at the twentieth 1 to 30, and after that about 1 to
36.5. In old age there is a further slight decrease in proportion. In
many men of great intellectual eminence the brain weight has been
large--Cuvier's brain weighed 64-1/2 oz., Goodsir's 57-1/2, for
instance--but the exceptions are numerous. Brains over 60 oz. in
weight are frequently found in quite undisting