Because of the nature of the arm's skeleton, a brief digression is in order on the subject of Kinematic Chains.

A Kinematic Chain is a line of bones, each one the parent of the next, which are linked together.  Kinematic chains are specified by using the 'Attach' button on the Bones toolbar.  This button will force the child bone to attach its base to the tip of its parent, and will kinematically attach the child to its parent.  Only one child may be kinematically attached to any given parent (even if many children have their bases attached to the parent's tip).

Also, any bones which are created by dragging from the tip of their parents (as you've been doing in this tutorial) are automatically attached to their parents, if there is not already a child bone attached to that parent.

The benefit of a kinematic chain is this:  whenever one bone in the kinematic chain is moved, all the other bones in the chain are also moved to accomodate the movement of the one.  This is done by a piece of the program called the 'Inverse Kinematics Engine'.  This is the thing that allows us to move the hand directly, rather than needing to manually rotate the bicep and forearm to get the hand into position.

However, there are times when you will not want a kinematic chain to continue all the way up a chain of bones.  The arm is one of those times:  since the shoulders rarely move, they should not be influenced by the motion of the other bones of the arm.  Currently, if you moved the hand, it would influence the shoulder.

Select the Right bicep, and click the 'Detach' button from the toolbar.

Now, if you moved the hand, the movement would only influence bones up to the bicep.  Because there is no attachment between the bicep and the shoulder, the kinematic chain does not proceed further up the hierarchy.

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