Uvula and Tonsils, Lobus Uvulx (Figs. 104 and ro6).—The uvula (uvula vermis) comprises a considerable part of the vermis inferior behind the nodule. It broadens backward and is widest next the pyramid. Bounded on either side by the sulcus val leculx, it projects into the valley like the uvula into the isthmus of the fauces. It comprises one large branch of the arbor vitro which bifurcates near its origin into two lamina; and presents at the surface six or eight small gyri. A slight ridge, the fur rowed band, joins it to the tonsil (tonsilla cerebelli) in the hemi sphere. From the furrowed band the tonsil expands downward and backward, forming a lobule of nearly a dozen sagittal gyri. The tonsil overhangs the side of the uvula and conceals the fur rowed band, medially; and, behind, it conceals the connecting ridge between the pyramid and biventral lobule. Its large size makes it a prominent feature of the human cerebellum. The fossa containing the tonsil is the bird's nest (nidus avis). Be hind the uvular lobe, composed of the above three lobules, is the prepyramidal sulcus.
Pyramid and Biventral Lobules, Lobus Pyramidis (Figs. 104 and ro6).—As seen from the surface, three or four distinct gyri make up the pyramid (pyramis vermis); in reality, it covers one strong lamina of the arbor vitm, which divides into the surface. It forms the most prominent lobule of the inferior worm. A low connecting ridge joins the pyramid to the biventral lobule in the hemisphere. The biventral lobule (lobu lus biventer) is triangular in outline. Its base looks toward the flocculus and is bounded by the post-nodular and the horizontal sulcus; its apex is continuous with the connecting ridge joining it to the pyramid. The gyri composing it radiate from the apex
toward the base, and are divided into two groups by a very deep intralobular sulcus. Its lateral extension is a little beyond the flocculus. The post-pyramidal sulcus bounds it postero-later ally, and separates it from the slender lobule.
Tuber Vermis, Slender and Inferior Semilunar Lobules, Lobus Tuberis (Figs. 104 and io6).—The tuber vermis forms the posterior end of the inferior worm. It resembles the lobules of the vermis superior, because some of its half dozen tertiary gyri are continued into the hemispheres, the sulcus vallecule not cutting them off. A bifurcated lamina of the arbor vitae enters into the tuber. The horizontal sulcus separates it from the folium vermis of the superior worm. The slender and inferior semilunar lobules comprise the posterior two-thirds of the in ferior surface of each hemisphere, extending from the biventral lobule to the postero-lateral border. Twelve to fifteen gyri compOse the lobules. The gyri are divided into three groups by the midgracile and post-gracile sulci; the anterior and middle groups are named the anterior slender and posterior slender lobules, they constitute the lobulus gracilis. The posterior is the inferior semilunar lobule. The inferior semilunar lobule, only, is continuous with the gyri of the vermis. The great size of the inferior and superior semilunar lobules is the most characteristic feature of the human cerebellum.
The gray matter of the cerebellum is composed of cortex which covers the,cerebellar laminm and of nuclei imbedded in the medullary body (Figs. io8 and 109).