Prominent folds of the brain are present in

a. cerebral medulla
b. white matter
c. cerebral cotex

The layer of cells which covers the cerebral hemisphere is called cerebral cortex and is thrown into prominent folds.

The cerebral cortex, a thin layer of gray matter forming the outer boundary of the cerebrum is 2-4 mm in thickness. Within this layer, countless neurons are meticulously organised into distinct layers. During prenatal development, as the brain undergoes rapid expansion, the gray matter of the cortex grows at an astonishing pace compared to the deeper white matter. Consequently, the cortical region undergoes transformation, folding and rolling upon itself, giving rise to characteristic features known as gyri or convolutions. These folds create deep grooves called fissures and shallower ones known as sulci. The most prominent of these fissures, the longitudinal fissure, divides the cerebrum into two cerebral hemispheres. Between these hemispheres lies the falx cerebri. Internally connecting the cerebral hemispheres is the corpus callosum, a broad band of white matter containing axons facilitating communication between the two hemispheres.