The cerebrum develops from two vesicles in the lateral walls of the prosencephalon, the telencephalic vesicles. In cyclostomes[1] and fish, the telencephalic vesicle is simple, containing only one cavity.  Only the olfactory bulbs are individualized. From amphibians to mammals, two hemispheres are generally recognized, with each having its own ventricle. Only in mammals do the hemispheres show a considerable increase in size, somewhat surrounding the diencephalon. phylogenetically, as the telencephalon grows, the olfactory bulbs regresses.


The cerebrum occupies the most rostral portion of the encephalon. It consists of two hemispheres separated by the medial longitudinal fissure (also known as the longitudinal cerebral fissure). The cerebrum's functions are to receive sensory signals and compare them with previous experiences, and to make decisions.


On the surface of each hemisphere there are folds called gyri, which are separated by sulci. The volume of the cerebrum and the number of sulci grew in parallel with each other during evolutionary development, allowing individual variations and variations between species.


Each cerebral hemisphere is composed of gray and white matter. The gray matter constitutes the cortex[2] and the basal nuclei, and the white matter is mainly composed of myelinated fibers.


[1] This name means a round mouth (from the Greek kyklos, circle”; stoma, mouth”) with a suction function rather than a masticatory one.

[2] From the Latin, cortex, “cover”.