The structure indicated is the trapezoid bone of the hand.
There are three groups of bones in the hand:
- Carpal bones (8 in total)
- Metacarpal bones
The carpal bones are separated into two rows:
- Proximal row
- Distal row
The trapezoid bone is located in the distal row of carpal bones. There are four bones in the distal row:
It’s easy to confuse the location of the trapezoid with the adjacent and similarly named trapezium bone. A way to remember where the trapezium is located is that trapezi-UM rhymes with thUMB, and therefore articulates with the 1st metacarpal of the thumb, the trapezoid bone lies just medial to it.
Learn more about the bones of the hand in this anatomy tutorial.