492 Dr Autson on Single and Correct Vision, by means of 
In answer to this, I would observe, first, that although there 
may be an anatomical difficulty in understanding how the sensa- 
tion and motion of the left side of the face are put in connection 
with the right side of the brain, yet observation of the effects of 
injury or disease demonstrate that they ave in connection with 
it; the palsy depending on injury or disease of the right side of 
the brain extending very generally to the left side of the face, as 
well as of the body. And secondly, I would say that there is no 
great difficulty in understanding that this should be the case, if 
we suppose, as Mr Mayo appears inclined to do,* that the true 
origin of the nerves is in those columns of the cerebro-spinal axis 
which do not decussate (and this is pretty certainly the case as to 
the fifth nerve, which is easily traced down into the spinal cord be- 
hind the Corpora pyramidalia), and that the decussating fibres of 
the Corpora pyramidalia are not to be considered as the continua- 
tion of the columns of the spinal cord, but as the cords of commu- 
nication between these columns, and the masses of the brain and 
cerebellum.t} If this be so, it is easy to conceive, that an injury of 
the right side of the brain, transmitted through these cords of com- 
munication, should strike downwards to the left side of the body, 
and upwards to the left side of the face in palsy ; and that, in the 
natural state, the sensation and motion of the left side of the face, 
as well as trunk and limbs, should be in connexion, although by 
a circuitous route, with the right side of the brain ; and therefore 
in harmony with impressions on the right optic lobe. 
If the foregoing speculation be just, it would seem that the 
structure to which the attention of physiologists was first directed 
by Newroy, is only a part of the arrangements, by which the in- 
* Outlines of Human Pathology, p. 202. 
+ “ The two cords of the spinal marrow do not cross, but merely the middle or 
pyramidal fasciculi of each, which give origin to the Crura cerebri by expanding and 
becoming broader." —Tiedemann’s Anatomy of the Fetal Brain, Translated by Ben- 
nett, p. 144. I am aware of the difficulty of tracing the course of the fibres at the 
medulla oblongata, and what Sir Cuares Bett describes, I believe correctly, decus- 
sating fibres behind the pyramids; but all are agreed that there are fibres in this 
part which do not decussate. 
