The structure indicated is the trapezium 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 trapezium bone is located in the distal row of carpal bones. There are four bones in the distal row:
The trapezium bone articulates with the 1st metacarpal of the thumb. It’s easy to confuse the location of the trapezium with the adjacent and similarly named trapezoid 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.
Learn more about the bones of the hand in this anatomy tutorial.