DEVELOPMENT OF PONS
The pons arises from the ventral part of the metencephalon. It also receives a contribution from the alar lamina of the myelencephalon, in the form of the cranial part of the bulbopontine extension. This extension comes to lie ventral to the metencephalon, and gives rise to the pontine nuclei. Axons of cells in these nuclei grow transversely to form the middle cerebellar peduncle.
As in the myelencephalon, the roof of the metencephalon becomes thin and broad. The alar and basal laminae are thus orientated as in the medulla.
The lateral part of each alar lamina (often called the rhombic lip) becomes specialised to form the cerebellum. The ventral part of the alar lamina gives origin to the sensory cranial nerve nuclei, and the basal lamina to the motor cranial nerve nuclei, of the pons as described.
The nuclei derived from the basal, and alar, laminae lie in the dorsal or tegmental part of the pons. The ventral part of the pons is constituted by:
a. Cells of the bulbopontine extension (derived from the alar lamina of the myelencephalon),form the pontine nuclei. Axons of the cells in these nuclei grow transversely and form the middlecerebellar peduncle.
b. Corticospinal and corticobulbar fibres that descend from the cerebral cortex, and pass throughthis region on their way to the medulla and spinal cord. Some fibres from the cerebral cortex terminate in relation to the pontine nuclei. These are the corticopontine fibres.