The Middlebury register and Addison County journal. [volume] (Middlebury, Vt.) 1883-1885, 1883-05-04
Why We Are

A suggestive paper in the Popular
Science Monthly is Dr.. w. G. Cahalr's
on a subject in which every one must
feel an interest, why Are We Right
handed?" No post-mortem examina-
lions have been made to clear up n
of his points-whether a certain
arrangement of blood vessels and the
use of the left hand do occur in the
same individual--but as to right
handedneSs he makes some convincing
statements. In the first place the
brain IS divided into two h%emispheres,
and the nerve force and nerve tibers
which produce muscular action on the
one side of the body have their origin
in the opposite hemisphere of the
brain. From the earliest period the
left hemisphere has been larger and
heavier than its counterpart, and the
convolutions of gray matter have been
more numerous on this side than on
the right. This superior development
he attributes to Il peculiar arrangement
OF the bloo1 vessels, by means of which
a greater hood supply is distributed to
the brain substance Of this side. That
arrangement is the manner of origin
of the right and left common carotid
arteries, the right being a branch of
the innominate artery, While the left
springs directly from the aorta. DIR.
Cahall then proceeds as follows to
further show that we are right-handed
because, as might be said, 1--WE are
left-headed :"
"This directness of communication,
in addition to a larger caliber of the
left carotid, gives the left hemisphere
a decided advantage in the race of de-
velopment. To reverse these state
ments we would have: AS a conse-
quence of the greater capacity of the
left carotid the left hemisphere of the
brain has Il greater blood-supply; as a
consequence, there is IA greater develop
ment of the left hemisphere as to
weight, bulk and number of convolu-
lions; as a consequence, when there is
need of muscular action the child
naturally uses those muscles which
possess the more powerful nerve-sup-
ply, for muscles are only strong in pro-
portion to their nerve-supply; as a con-
sequence, the nervous energy is dis
patched, in those cases where they can
be a choice, from the left hemisphere;
as a consequence, the right hand and
the right leg will be more likely used,
since this side of the body is innervated
by the left hemisphere. Thus, predis-
position primarily, and use afterward,
influencing and strengthening each
other, fix upon ii habit almost unchange-
able-hOw firmly, let those whoever
attempted to break the habit in a left
handed boy testify. But this leads to
another question. Why are there left
handed people? Before we answer this
question we will again look at the dia-
gram. We have seen that, as the aorta
rises from the heart. it arches from
right to left; and the first large artery
it gives off is the innominate, which in
turn is divided into the right common
carotid and right s%ubelavian arteries.
Further on we find the left common
carotid and the left s%ubclavian arteries
arising separately from the aorta.
Now, in making their dissections,
ANTAGONISTS have found that in a GER
tain proportion of their subjects the
aorta arches from left to right, in which
case the innominate is on the left side
and the common carOtic and subclavian
separate on the right. This arrange
ment would favor the growth of the
right hemisphere and would predispose
to the use OF the left hand"