Bidextrous grasp appears at:
16 weeks - Tries to reach cube, but overshoots and misses. 20 weeks- Able to grasp voluntarily, Bidextrous approach 24 weeks- More mature grasp, Drops one cube when another is given. 28 weeks- Unidextrous approach, Bangs cube on table. Transfers. Retains one when another is given. Ref: Illingwoh's " The development of young child and infant" - page 278.
3 months
4 months
5 months
6 months
General anatomy