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When that pair is set in action, the post-fulcral end of the head lever is tilted downwards, while the pre-fulcral end, on which the face is set, is turned upwards. The complex muscles thus tilt the head backwards and the face upwards, but where are the muscles which serve as their opponents or antagonists and reverse the movement?
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.
Here we seem to come across a defect in the human machine, for the greater straight muscles in the front of the neck, which serve as opposing muscles, are not only much smaller but at a further disadvantage by being yoked to the pre-fulcral end of the lever, very close to the cup on which the head rocks.
In creating a movable joint for the head, then, a safe passage had to be obtained for the medulla that part of the great nerve stem which joins the brain to the spinal cord. The medulla is part of the brain stem. This was only one of the difficulties which had to be overcome. The eyes are set on the pre-fulcral lever of the head.
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.
It will be convenient to call that part of the head which is behind the ear passages the post-fulcral, and the part which is in front the pre-fulcral. Now the face is attached to the pre-fulcral part of the lever and represents the weight or load to be moved, while the muscles of the neck, which represent the power, are yoked to the post-fulcral end of the lever.
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