Crebellum Structure

The cerebellum is situated in the posterior cranial fossa (Fig 1), between the tentorium cerebelli which separates it from the occipital lobe superiorly and foramen magnum. It lies dorsal to the pons and medulla, and is separated from them by the fourth ventricle at its median region. The first accurate description of human cerebellum was given by Ziehen in 1934(25), prior to that most of the descriptions of cerebellum were based on dissection of animal cerebellums(26). The cerebellum is somewhat ovoid in shape with constriction at its median part. The shape of the human cerebellum differs from most other mammals, most obvious features being its overall size, medial to lateral width, depth of transverse fissures and the parallel orientation

In the classic nomenclature(28) the vermis and hemisphere of the cerebellum is divided into three lobes namely anterior, posterior and flocculonodular lobe (Fig 2 and 3), by two deep fissures known as the primary fissure between the anterior and posterior lobes and the posterolateral fissure between the tonsil and flocculonodular lobe(24,25). The anterior lobe is bound anteriorly by superior medullary velum and posteriorly by the primary fissure. The vermis and hemispheres in the anterior lobe are further divided into lobules by two fissures namely precentral fissure and the preculminate fissure. The vermis is divided into three lobules namely lingula, central lobule and culmen. Lingula and the central lobule separated by the precentral fissure, central lobule and the culmen separated by the preculminate sulcus. The hemispheric connection of the central lobule is known as the ala and that of the culmen is known as the anterior quadrangular lobule. The lingula is generally considered not to have any hemispheric extension(27–29). The paramedian sulcus on the anterior lobe is shallow and there is a smooth transition from vermis to the hemisphere hence the hemispheric portion of the anterior lobe is sometimes called simple lobule(27). At the paramedian sulcus though grossly it may appear the vermis to be in continuity with the hemisphere there may be discontinuation of the cortex and the white fibres may be exposed at these regions, more so in the posterior lobe where the paramedian sulcus is prominent and deep(27).The posterior lobe is bounded by the primary fissure anteriorly and posterolateral fissure posteriorly, vermis of the posterior lobe has 5 lobules namely declive, folium tuber, pyramid and