being yoked to the pre-fulcral end of the lever, very close to the cup
on which the head rocks. However, if the _greater straight_ muscles lose
power by working on a very short lever, they gain, in speed; we set them
quickly and easily into action when we give a nod of recognition. All
the strength or power is yoked to the post-fulcral end of the head; the
pre-fulcral end of its lever is poorly guarded. Japanese wrestlers know
this fact very well, and seek to gain victory by pressing up the poorly
guarded pre-fulcral lever of the head, thus producing a deadly lock at
the fulcral joint. Indeed, it will be found that those who use the
jiu-jitsu method of fighting have discovered a great deal about the
construction and weaknesses of the levers of the human body.

Merely to poise the head on the atlas may seem to you as easy a matter
as balancing the beam of a pair of scales on an upright support. 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. In creating a
movable joint for the head, then, a safe passage had to be obtained for