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The neural groove is converted into neural tube. The stages in the formation of neural tube do not proceed simultaneously all over the length of the neural plate. The middle part is first to become tubular so that for sometime the neural tube opens cranially and caudally.

The neural tube is divisible into enlarged cranial part and a caudal tubular part. The enlarged cranial part forms the brain. The caudal tubular part forms the spinal cord. The cavity of developing brain shows three dilatation craniocaudally, these are prosencephalon, mesencephalon and rhombencephalon. The prosencephalon becomes divided into telencephalon and diencephalon. Telencephalon contains right and left telencephalic vesicles. The rhombencephalon also becomes subdivided into a cranial part the metancephalon and a caudal part the myelencephalon. Parts of the brain that are developed from each division are as follows–

PROCENCEPHALON– Telencepehalon- cerebral cortex

corpus striatum

— Diencephalon– Thalamus, hypothalamus, optic stalk, pars distalis and nervosa of hypophysis

MESENCEPHALON——–midbrain RHOMBENCEPHELON— Metencephalon- pons and cerebellum

—-Myelencephalon- Medulla oblangata

The prosencephalon, mesencephalon and rhombencephalon are at first arranged cranio-caudally. The relative positions are altered by the appearance of number of flexures.

a) THE CERVICAL FLEXURE- At the junction of rhombencephalon and spinal cord.

b) THE MESENCEPHALIC FLEXURE- In the region of midbrain.

c) THE PONTINE FLEXURE- At the middle of rhombencephalon dividing into metancephalon and myelencephalon.

d) THE TELENCEPHALIC FLEXURE- That occurs much later between telencephalon and diencephalon.