Development of brain in frog

Development of Brain
The anterior part of neural tube is distinguished as encephalon which develcps into various parts of the brain through thickening, thinning, evagination and invagination.
Primary Divisions of Encephalon :
The encephalon divides into three distinct regions - prosencepha Ion (forebrain), mesencephaIon (midbrain) and rhombencephalon (hindbrain). The cavities of the three primary divisions are known as prosocoel, mesocoel and rhombocoel Prosencephalon constricts further into an anterior endbrain or telencephalon and a 'tween' brain, the diencephalon. At the posterior limit of prosencephalon, the brain bends ventrally around the anterior ond of the notochord to form a cranial flexure which remains as a prominent feature of brain in vertebrates. The area of cranial flexure thickens to develop the tuberculum posterius that marks the posterior limit of forebrain ventrally. The anterior limit of telencephalon is the lamina terminalis Nhich will separate the future cerebral hemispheres by a longitudinal groove. Actually, the lamina terminalis represents the anterior fused ieuroporal area. Telencephalon will differentiate into a pair o: lobes calla( cerebrum. They enclose a cavity called telocoel which expands laterally to give rise to lateral ventricles communicated by way of tubt.lar Foramen Monro. The roof of the cerebral lobes thicken to give rise to cortex or pallium, the floor and sides of which form the corpora striata. The olfactory lobes arise as a pair of evaginations from the anteroventral part of telencephalon. Subsequently, they become fused mesially. The nerves originating from the olfactory lobes innervate the nasal epithelium al olfactory placode. The ventricle enclosed by the olfactory lobe is called olfactocoel . In the floor of diencephalon, anterior to tuberculum posterius, there  deVelops a vesicular evagination called infundibulum. Later, the stomodaeal outgrowth called hypophysis is separated and connected to infundibulum to form the pituitary gland The cells of infundibulum give rise to posterior pituitary (pars netSrosa) and the hypophysis develops into anterior pituitary (pars distalis , pars intermedlii and pars tuberalis). Between the infundibulum and the tuberculuto posterius, there is another posteriorly directed pocket called mammillary recess.
A pronounced thickening appears in front of the infundibuluni called optic chiasma. A depression is developed anterior to the optic chiasma known as optic recess. In front of the optic -ecess, there appears a ventral thickening called torus transversus. The ventricle inside diencephalon transforms into diocoel or third ventricle communicating with lateral ventricle by Foramen Monro The roof of the diencephalon anterior to mesencephalon, develops a saccular outgrowth known as epiphysis which becomes separated froni the brain as a small knob of cells differentiating into the brow spot of the adult frog. It represents the pineal gland of higher vertebrates. The rout of the diencephalon becomes non - nervous and vascular structure which hangs into the diocoel as a much folded anterior choroid plexus. A Between anterior choroid plexus and epiphysis, there are  ganglion and a commissure. The optic vesicles arise as ventro - lateral evaginations of t diencephalor and they differentiate into optic cup. The nervous elemen of the retina of eye will join with the optic chiasma of diencephalon.
Mesencephalon (Midbrain) The dorso - lateral thickenings of mesencephalon become th optic lobes cr corpora bigemina which are subdivided by a media fissure. The nerve tracts are found within ventro - lateral thickening the walls and floor of mesencephalon on either side of tuberculu posterius called crura cerebri which function as a pathway between for and hindbrain. The neurocoel of this part of brain modifies into mesocoi or iter (Aqueductus Sylvius) connecting 4th ventricle or rhomboc with third vertricle.
Rhombencephalon (Hindbrain) In higher vertebrates, rhombencephalon subdivides int metencephabn and mylencephalon, but there is no such modification amphibian b-am. There appears a slight transverse thickening in th anterior part of rhombencephalon which differentiates into cerebellum.Posterior to this, the roof of hindbrain develops into a thin, folded and vascular region called posterior choroid plexus. The ventral and ventro Literal walls of the rhombencephalon give rise to medulla oblongata.The rhombocoel modifies into fourth ventricle which connects posteriorly with central canal of the spinal cord.