[JesseK]

It's possible to put both the shoulder and 'wrist' motors very low. For the shoulder joint, it's a simple chain/belt run. For the wrist joint, you can run chain/belt up to the axle of the shoulder joint, use sprockets that have bearings inside them and are attached to each other, then run chain/belt to the wrist.

The sprockets for the wrist spin independently of the orientation of the shoulder (due to the bearings), which is why this works. It also keeps the heavier components (motors and transmissions) as low as possible.