A : Cerebrum. If you said "forebrain" you are still correct, but a part of the forebrain is still hidden in this picture. The forebrain is called prosencephalon in Latin, as also in embryological terms. It includes the telencephalon. Telencephalon= "end brain" - the most rostral part of the neural tube. It really balloons out, as two telencephalic vesicles, on two sides from the rostral end of the tube.

The other part of the forebrain, the diencephalon, formed by the thalamus, hypothalamus, epithalamus and metathalamus (geniculate bodies) is still hidden by the telencephalon in this picture.

What we see here is the surface of the cerebrum, the cerebral cortex. It is grey matter, thrown into numerous folds called gyri (singular : gyrus) separated by grooves called sulci (singular : sulcus). Some deeper sulci are also called as fissures. The terms sulcus and fissures are sometimes used interchangeably.

B : Midbrain. Or mesencephalon, which means the same thing!

C : Pons.

D : Medulla oblongata. (Well, the oblong medulla!)

The pons is the embryonic metencephalon, the medulla oblongata the myelencephalon. Together the two are known as rhombencephalon, from the rhomboid shape of the fourth ventricle.

E : Cerebellum. The grey matter of the cortex is thrown into fine, somewhat parallel folds like thick leaves, and hence called "folia".