Final answer:
The movement where the thumb touches the tip of the little finger is called opposition, facilitated by a saddle joint which allows flexion and abduction of the thumb.
Step-by-step explanation:
The movement of the thumb to touch the tip of the little finger is called opposition. This action is facilitated by the unique saddle joint at the first carpometacarpal joint, which allows the thumb to move across the palm to meet the other fingers. This joint is formed between the trapezium carpal bone and the first metacarpal bone of the thumb. The opposition movement is a combination of flexion and abduction at this joint. After opposing, moving the thumb back to its normal position adjacent to the index finger is known as reposition.