WORM HEMISPHERE Pyramis Lobulus biventer Uvula Tonsilla Nodtiltis . Flocculus The pyramid, separated from the tuber vermis by the sulcus postpyramidalis, connects the biventral lobule of the one side with that of the other. A fissure splits each lobulus biventer into two portions, an anterior medial and a posterior lateral.
The tonsilla is embraced by a medially concave curve described by the sulcus firaeftyramidalis, which separates the pyramis from the uvula.
In advance of the uvula lies a small conical structure, the nodulus. Immediately in front of the latter is a thin white sheet, the velum medullare posterius, that continues laterally on each side as the fiedunculi fi'occuli to join the flocculus. Lateral to the latter, between the lobulus quadrangularis of the superior lobes and the lobulus biventer is seen the accessory flocculus, flocculus secundarius.
On removing the tonsil, a broad lamella, the ala uvulae, or the furrowed band, is seen pass ing outward from the uvula. The posterior margin of this band is free, its anterior one is continuous with the posterior medullary ve lum. The deep recess, whose floor is formed by the ala uvulae and the velum medullare posterius, lodges the tonsil and is called the nidus avis. Its lateral wall is contributed by the lobulus biventer and the pedunculus flocculi, while it is bounded medially by the uvula and behind by the pyramid. The lobulus biventer forms the lateral, the tonsil the medial and the flocculus the anterior part of the lobus inferior.
The foregoing relations are recapitulated in the following table: On sectioning the cerebellum, we recognize the internally situated white medullary substance, the corpus medullare, and the substantia corticalis, which invests the periphery as a thin continuous band of gray matter. The medullary substance of the cerebellum is composed of that of the hemispheres and of the worm, which are continuous medially.
Stout tracts of medullary substance, the laminae medullares, pass outward from the medullary centre and send off, mostly at acute angles, secondary medullary laminae. The latter, in turn, give off still smaller sheets, which finally are enclosed by gray substance and represent the cerebellar convolutions or folia, the gyri cerebelli. This structure, when viewed in sagittal sections, is known as the arbor medullaris, on account of the tree-like branching. In sagittal sections through the worm, where this delicate figure is particularly well seen, it is called the arbor vitae vermis.
The medulla of the hemispheres is con nected with neighboring parts of the brain by masses of nerve fibres. These masses constitute more or less robust columns, which are termed the peduncles, crura or brachia of the cerebellum and serve to connect it with the pons, the mid-brain and the medulla oblongata.
The brachia pontis, middle cerebellar peduncles, or crura cerebelli ad pontem, emerge on each side from the horizontal sulcus at the anterior border, between the lobulus quadrangularis, tonsilla and flocculus, and pass convergingly forward, to blend with the pons.
The crura cerebelli ad cerebrum or superior cerebellar peduncles, also known as the crura cerebelli ad corpora quadrigemina, and the brathia..cortiunctiva cerdelll, lie in front of the pontile crura, pass as flattened cylindrical columns convergingly forward and disappear beneath the quadrigeminal bodies. The velum medullare anterius stretches out between them.
The crura cerebelli ad medullam oblongatam or inferior cerebellar peduncles, also often called the corpora restiformia, pass out between the foregoing cerebellar arms and turn sharply backward and downward into the medulla oblongata.