Mammalian brain differs from an amphibian brain in possessing

Options

A. olfactory lobes
B. corpus callosum
C. cerebellum
D. hypothalamus

Answer

### Step-by-Step Solution

1. **Understanding the Question**: The question asks how the mammalian brain differs from the amphibian brain. Specifically, it is looking for a unique structure or feature present in mammals but absent in amphibians.

2. **Identifying Key Features of the Mammalian Brain**: One of the key features that distinguishes the mammalian brain is the presence of the corpus callosum. This is a significant structure that connects the left and right cerebral hemispheres.

3. **Defining the Corpus Callosum**: The corpus callosum is a wide, thick nerve tract made up of a flat bundle of commissural fibers. It is located beneath the cerebral cortex and plays a crucial role in interhemispheric communication.

4. **Comparing with the Amphibian Brain**: Amphibians do not possess a corpus callosum. Instead, they have other commissures, such as the anterior commissure, which connect the two halves of the brain but are not as complex or developed as the corpus callosum found in mammals.

5. **Conclusion**: Therefore, the main difference between the mammalian brain and the amphibian brain is the presence of the corpus callosum in mammals, which facilitates communication between the two hemispheres of the brain.

### Final Answer
The mammalian brain differs from the amphibian brain in possessing the **corpus callosum**.