Here's a breakdown:
Whale Pectoral Flipper:
* Function: Used for steering, propulsion, and balance in the water.
* Structure:
* Bones: Similar bone arrangement to a human arm: a single long bone (humerus), two bones in the forearm (radius and ulna), and a series of wrist bones followed by finger bones.
* Muscles: Powerful muscles that help move the flipper.
* Skin: Smooth and streamlined for efficient movement in water.
Horse Foreleg:
* Function: Used for walking, running, and supporting the weight of the horse.
* Structure:
* Bones: Similar bone arrangement to a human arm: a single long bone (humerus), two bones in the forearm (radius and ulna), and a series of wrist bones followed by finger bones (the horse only has one large toe that bears the weight).
* Muscles: Powerful muscles that support the weight and propel the horse.
* Skin: Covered in hair, with hooves at the end of the foreleg.
Homology:
* The similar bone structure in whale flippers and horse forelegs is evidence of their common ancestor. This ancestor likely had four limbs that were used for walking on land. Over time, these limbs evolved into the specialized structures we see in whales and horses.
* This homology highlights the power of evolution to modify structures for different functions while retaining underlying similarities.
In summary: While whale pectoral flippers and horse forelegs have very different functions and appearances, they share a common underlying skeletal structure, revealing their shared evolutionary history.