Re: Number of bones in hand, smallest bone in body?

The number of bones an appendage has determines the number of joints in that part of the body, and this determines the amount and type of movement that the appendage can do. For arms and legs, which have limited movement compared to fingers, there are very few joints, while fingers, which have extensive movement, have many joints. Each finger (except the thumb) has three bones, called phalanges, which allow the fingers to curl all the way around and contact the palm. This allows primates, including humans, to grasp things tightly in their hands, especially when climbing. If each finger had only one bone, it would be very difficult to do many things, like writing, typing, climbing, or even holding heavy objects.

From an evolutionary perspective, the number of bones in the hands (8 carpals in the wrist, 5 metacarpals in the palm, and 2-3-3-3-3 phalanges in the fingers make 27 bones per hand) is directly related to the origins of the limbs. When the first Paleozoic fish began venturing onto land, they used modified fins to maneuver around. With the rise of the true amphibians, the bones and rays of the pectoral and pelvic fins became the bones of the arms and hands, and legs and feet. The organization of the bones in the limbs has changed very little from the original fishy fins; from proximal (nearest the body) to distal (furthest from the body) the order is: 1 bone -> 2 bones -> a cluster of tiny bones -> 5 sets of "rays" which form the palm and fingers.

To answer the next question, there are some really tiny bones found in the ear. The three bones which transmit sound from the eardrum to the cochlea (inner ear) are the smallest bones in the body.