The structure indicated is the proximal phalanx of the 5th finger.
The hand consists of three groups of bones:
The phalanges (phalanx = singular), form the fingers/digits of the hands. The thumb consists of two phalanges: proximal phalanx and distal phalanx. The rest of the fingers consist of:
- Proximal phalanx
- Middle phalanx
- Distal phalanx
The phalanges themselves have the following features:
- Base (proximally)
- Head (distally)
- Shaft/body (in between the base and the head)
Learn more about the anatomy of the bones of the hand in this tutorial.