I am
now going to show that a great number of difficulties had to be overcome
before our heads could be safely poised on our necks. The head had to be
balanced in such a way that through the pivot or joint on which it rests
a safe passageway could be secured for one of the most delicate and most
important of all the parts or structures of the human machine. We have
never found a good English name for this structure, so we use its clumsy
Latin one--_Medulla oblongata_--or medulla for short. In the medulla are
placed offices or centres which regulate the vital operations carried
on by the heart and by the lungs. It has also to serve as a passageway
for thousands of delicate gossamer-like nerve fibres passing from the
brain, which fills the whole chamber of the skull, to the spinal cord,
situated in the canal of the backbone. By means of these delicate fibres
the brain dispatches messages which control the muscular engines of the
limbs and trunk. Through it, too, ascend countless fibres along which
messages pass from the limbs and trunk to the brain.
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