How to select all the bone descendants in armature.

 The goal: To select all the bones, specifically the left wrist + it's descendants.

1) Select one of the bone in wirst.L

2) Go to Pose Mode

3) Press A 

4) Press Ctrl to deselect the bones that you do not wish to select.

Optionally, you can use the "Select Pattern" option to select object with specific patterns. For example, if you want to select bones with .R pattern.

1) Select the armature

2) Go to Edit Mode

3) Go to Select menu

4) Select "Select Pattern"

5) Type "*.R" to select bones with .R in their names