How are Organisms Structurally Similar? When examining internal structures of different species, you may notice there are similarities in the skeletal structures of some appendages even though the appendages have different functions. These types of structures are referred to as homologous structures, and they have been derived from common ancestors. Analogous structures have the same function but are not derived from some common ancestor. Vestigial structures are structures that seem to have no apparent use, but provide evidence of some past function. For example, some snakes have a remnant pelvic girdle.This pelvic girdle was used to attach appendages that snakes no longer have. Procedure Examine the structures in Figure 2.4 and answer the following questions: humerus ulna radius carpala metacarpals phalanges Bat Dolphin Sheep Human FLYING SWIMMING RUNNING GRASPING Figure 2.4: Bone structure and appendage function 1. Are there differences in the functional uses of these appendages? 2. List the functions of these appendages 3. Compare the humerus of the human with the dolphin. How are they different? 4. When comparing the humerus of the human with the dolphin, how are they similar? Describe the changes in phalange structure and how these changes relate to the mode of locomotion for each animal. 5. 6. Now think about vestigial structures, and name five possible vestigial structures found in humans.