When organs of different organisms who are too different and do different activities but looks to be same, it is called homogous organs.

**Homologous organs**

Homologous organs refer to the organs that have a similar structure but may have different functions in different organisms. These organs are believed to have evolved from a common ancestor and have undergone modifications over time to adapt to different environments and perform different functions.

In the case of the forelimbs of frog, lizard, bird, and man, they all have a similar basic structure despite their different functions. They all have bones, joints, and muscles, although the sizes and shapes of these structures may vary.

**Explanation:**

1. **Bones**: The forelimbs of frog, lizard, bird, and man all have a similar arrangement of bones. They consist of a humerus (upper arm bone), radius and ulna (lower arm bones), carpals (wrist bones), metacarpals (palm bones), and phalanges (finger bones). The number and length of these bones may differ, but the basic structure remains the same.

2. **Joints**: The forelimbs of these organisms also have similar joint structures. They all have hinge joints at the elbow and ball-and-socket joints at the shoulder. These joints allow for flexibility and movement in different directions.

3. **Muscles**: The muscles present in the forelimbs of these organisms also show similarities. They are responsible for the movement and control of the forelimbs. Although the size and strength of these muscles may vary, the basic arrangement is similar.

**Evolutionary Relationship:**

The presence of homologous organs in these different organisms suggests that they share a common ancestor. Over time, as these organisms diverged and adapted to different environments, their forelimbs underwent modifications to suit their specific needs and functions.

For example:

- The forelimbs of frogs are adapted for swimming and jumping, with long and muscular legs for propulsion.
- Lizards have forelimbs adapted for climbing, with strong and flexible toes for gripping surfaces.
- Birds have forelimbs modified into wings for flight, with feathers and specialized bones to support and control their aerial movements.
- Humans have forelimbs adapted for fine motor skills and manipulation, with opposable thumbs and dexterity for tool use.

Despite these differences in function, the underlying homologous structure of the forelimb suggests a common evolutionary origin. This concept of homology supports the theory of evolution and provides evidence for the relatedness of different species.