Primate Anatomy

All primates have five fingers on each hand. They also have nails instead of claws. However, there are some primates who have a combination of nails and claws. In order to be a primate, an animal must have at least one nail. 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. (click these pictures to see enlarged images)

Try and hold any object, such as your pen without using your thumb. Not very easy, is it?

Are there any other animals you can think of that can hold objects in their hands? List several advantages that humans have, due to our ability to grasp objects?

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. A dog cannot lift his front legs out to the side of his body.

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Clavicle-Shoulder Activity
Without a clavicle your arm motion is restricted to forward and backward movement only. Try the following activities and note what must be done to accomplish them, if possible.
1. Try touching the chair next to you.
2. Pat your head and rub your stomach.
3. Clasp hands together. Compare pulling hands apart with elbows.

What activities would be improved by moving the arms into many positions? List several activites you do that require having your arms placed out to the side of your body.

The forearm in primates contains two separate bones, the ulna and the radius. These two bones rotate around each other, allowing the palm of your hand to be turned up and down. The ulna and radius are one bone in the dog, therefore the dog cannot turn his paw upwards.

Why do you think dogs only have one bone instead of two in their forearm?

Forearm Rotation Activity

1. Pick up the computer's mouse and look at the underside. Note how your forearm rotated. Try it again without using forearm rotation.

2. Pretend you are picking up and eating an apple. How would you go about eating the apple if you could not turn your hand towards your mouth?

What is the advantage of having one bone instead of two in your forearm? How does forearm rotation aid primates in gathering and eating food? What other activities can you think of that requires the rotation of the arm?

Primate feet illustrate their dependency upon climbing. Compare these views: