NEET Class neet Answered

The corpus callosum is found only in placental mammals, while it is absent in monotremes, marsupials, and other vertebrates such as birds, reptiles, amphibians and fish.

There are 12 pairs of cranial nerves in higher vertebrates (reptiles, birds, mammals), while lower vertebrates (fishes, amphibians) have 10 pairs. 

Therefore, the correct answer is option (2) a, c

The X and Y brain samples may be from reptiles and birds, while the Z brain sample is surely from a mammalian.