The thumb is separated from the other fingers . This allows the thumb to be brought into opposition with the other fingers. An opposable thumb improves the ability of primates to securely grasp objects in their hands. As you can imagine, climbing on small branches would require the hand to be able to tightly grasp the branch. Opposable Thumb Activity Try and hold any object, such as your pen without using your thumb.
All primates have a clavicle.
Notice that the dog does not have one. The clavical bone helps keep the arms out to the side of the body. The presence of the clavical in primates contributes to the mobility of the shoulder. The arms of primates can move in many directions. In dogs, the mobility of the arm is limited to forward and backward movements.