HISTOGENESIS OF MESENCEPHALIC TEGMENTUM IN GOAT FOETUSES

Prenatal histogenesis of the mesencephalic tegmentum was studied using 46 goat foetuses ranging from 2.5 cm CRL (40 days of gestation) to 41.5 cm CRL (full term).  Standard procedures were adopted for histoarchitectural studies.  Neuroepithelial cells occupying the mesencephalic tegmentum of foetal goat brain differentiated during the seventh week of gestation. In the basal plate region, neuroblasts aggregated to form nuclei during the same age.  Tegmentum contained network of fibres and cells representing the reticular formation.  The development of mesencephalon was dependent on the differentiation of other parts of brain.  During third month, mesencephalic nucleus of trigeminal nerve, nuclei of oculomotor and trochlear nerves, tegmental nuclei, red nuclei and the substantia nigra were developed.  Nissl granules started appearing in neurons of the midbrain tegmentum by the middle of fourth month.  Ependyma lining the aqueduct was adult-like during fifth month. Myelination also began at this stage.  All the nuclei constituting midbrain architecture were well developed by term. Cells of the red nucleus were one among the largest neurons that could be seen in the entire brain.  The rubrospinal tract arising from the red nucleus is a major pathway of the extrapyramidal system and is of particular importance in domestic animals in postural control and locomotion.