The structure indicated is the proximal phalanx of the 5^th finger.

The hand consists of three groups of bones:

1. Carpals
2. Metacarpals
3. Phalanges

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.