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Inferior Surface of the Cerebellum

sulcus, lobule, flocculus, worm, velum and figs

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INFERIOR SURFACE OF THE CEREBELLUM The inferior surface of the cerebellum (facies cerebelli inferior) is prominent laterally and depressed centrally (as the organ is viewed inverted), the hemispheres being separated by the antero posterior groove, called the vallecula cerebelli (Figs. 102 and 1o6). The vallecula (little valley) is occupied by the inferior worm and is bounded on either side by a small cleft, between the worm and the overhanging hemisphere, called the sulcus vallecule. The inferior cerebellar surface is limited by the horizontal sulcus and is separated from the medulla by the transverse fissure of the cerebellum. It is more complex than the superior surface; and its sulci are more sharply curved forward as they pass from the worm into the hemispheres.

Sulci of Lower Surface (Fig. 1o6).—The interlobular sulci of this surface are very deep. They are three in number, namely: 1. The post-nodular sulcus (s. post-nodularis) (Figs. 102, and 1o6) is in the anterior end of the worm between the nodule and uvula. In the hemisphere it winds forward and outward between the inferior medullary velum and the tonsil and then continues lateralward between flocculus and biv entral lobule to the horizontal sulcus. It is the first cerebellar sulcus to be developed (Cunningham).

2. The prepyramidal sulcus (s. prcepyramidalis) (Figs. 104 and 1o6), situated between the uvula and pyramid, is very con cave in the hemispheres. It curves outward and forward around the tonsil, separating it from the biventral lobule. It terminates behind the flocculus in the post-nodular sulcus.

3. The sulcus (s. (Figs. 104 and 1o6), between the pyramid and tuber vermis, is near the posterior end of the worm. It forms an oblique groove in either sulcus valleculx, from which three concentric sulci extend into the hemisphere. The anterior of the three (the pregracile), usually considered the post-pyramidal sulcus in the hemisphere, separates the biventral lobule from the slender lobule (1. gracilis);

the remaining two (mid-gracile and post-gracile) subdivide the slender lobule into anterior and posterior slender, and separate the lobulus gracilis from the inferior semilunar lobule. The last is bounded behind by the horizontal sulcus.

Lobes of Lower are not continuous from the worm to the hemisphere as on the upper surface (Figs. Ioi and io6). Excepting in the posterior lobe, only a small ridge be neath the sulcus valleculm joins the central' and lateral lobules together. The inferior lobes are four in number. Each is composed of a central and two lateral lobules as on the upper surface. The lobule in the worm gives its name to the lobe.

Nodule and Flocculi, Lobus Noduli (Figs. 104 and nodule (nodulus vermis) is a small lobule at the anterior end of the inferior worm. It is composed of three or four gyri, which project from the middle of the dorsal surface of the inferior med ullary velum. It comprises a single branch of the arbor vitae. Though larger it is the counterpart of the lingula on the superior velum. It is bounded by the sulcus valleculm on either side. The inferior medullary velum extends laterally from the nodule and in part blends with the brachium pontis of the cerebellum. In front of the tonsil a layer of gray matter (peduncukisfloccu/i) appears on the velum. That gray matter enlarges more laterally to a small tufted mass, called the flocculus, in which the velum ends. Embryologically, the flocculus is the oldest lobule of the human cerebellum, as is the floccular sulcus (post nodular sulcus) which bounds it, the first one formed. The flocculus is very small and rudimentary in man. It is divided into an anterior and a posterior part, the latter being called the secondary flocculus. The flocculus is separated from the tonsil and the biventral lobule by the post-nodular sulcus. The whole line of structures, namely, the nodule, velum, peduncle and flocculus, form the lobe of the nodule.

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