The 'GIF'ted Cellist for Bow
The animated GIF is great for focusing on the precise mechanism of the many formatted motions that we make when playing the cello. Here is a bow technique primer illustrated GIF-style.
(See also The 'GIF'ted Cellist for Left Hand)
A Flexible Bow Hold
The following GIFs demonstrate the bow hold, and some flexibility exercises to make sure that hold is functioning properly.
First we place a naturally draping hand on the bow at the frog.
Note the natural and gentle dangle of the wrist here, and how the natural shape and spacing of the fingers transfers to the bow.
Here is a more specific demonstration of the exact placement of the fingers in front - 4 on the dot, 3 on the ferrule, 2 on the hair, 1 on the wire.
Here is the placement of the thumb, on the stick, up against the "doorstop" of the frog
The fingers on the bow serve as the landing gear for the arm on the string, and therefore they must be strong, but always flexible. Here are some exercises to develop flexibility.
First, the push-up.
Notice the play in all joints, from the wrist to the three ridges of knuckles. You can also see that the fingertips stay resting at the hairline around the ferrule, and find purchase against the outward fluting at the base of the frog.
Here is the push-up from the side view.