These lobules of the inferior portion of the median lobe serve to connect others of the lateral hemispheres. The spigot connects the almond-like lobes; the pyramid the biventral and the slender lobes.
Posterior to the pyramid are a series of la whim which extend to the posterior notch and form its floor. These pass directly from one side to the other, their free margin being con vex and directed backwards. They connect the posterior inferior lobes. And some of the most anterior of them, which do not project to the surface, connect the slender lobes as well as some of the anterior lamin of the posterior inferior lobes. These latter laminm of the in ferior vermiform process, Reil distinguishes by the name of tong and hidden commissure ( langen verdeckten Commissur ), and the former constitute his short and exposed commissure (Kurzen und sichtbaren Commissur).
Above the last-named commissure is a single lamina which forms a line of demarcation be tween the infetior and the superior vermiform processes, serving to connect the upper and posterior lobes of the hemispheres. This is the single commissure (eilfache quer Commissur).
It will serve to elucidate the foregoing neces sarily intricate description, if I sum up with the following enurneration of the lobes of the hemispheres, specifying at the same time the commissures by which they are connected, i. e.
the lobes of the superior and inferior vermiform processes which serve that purpose.
1. On the superiorsurface of the hemispheres.
a. The square lobes, consisting of eight lobules, which are connected by as many, or nearly so, of the superior vermiform process.
b. The upper and posterior lobes, connected by the single commissure, to be sought for on the floor of the posterior notch.
2. On the inferior surface of the hemi spheres.
a. The amygdale, united by the spigot.
b. The biventral lobes.
c. The slender lobes.
The biventral lobes and the anterior laminm of the slender lobes are united by the pyramid.
d. The posterior ilferior lobes, connected by the short and exposed and the long and hidden commissures.
The flocks or lobules of the pneumogastric nerve, ( lobule of the auditory nerve, Foville,) which are situate altogether anterior to the hemispheres and attached to each crus, are united by the posterior medullary velum, and through it appear to have some connection with the most anterior portion of the inferior vermi form process.
A vertical section of either hemisphere of the cerebellum or of its median lobe displays its structure, and serves further to demonstrate the subdivision into lobes above described.
When either hemisphere is cut in the vertical direction, the surface of the section displays a beautiful ramification of fibrous matter, the smaller branches of which are enveloped by laminw of grey matter. This appearance has such a resemblance to the trunk of a tree with its boughs and branches, that it early received and has continued to retain the name of arbor vile. The trunk of the tree is represented by a central nucleus of white matter, from the upper and lower surfaces of which branch off; some at a right, others at an acute angle, several laminw, each of which forms the parent stem of a number of other branches. Each of the primary branches is the foundation or cen tral stem of a lobulc. Lamin of fibrous mat ter are seen bmnching from both sides of it immediately after its separation from the nu cleus. Sometimes the primary branch bifur cates, and each division of it forms the sten of what may be called a sub-lobule. The ul timate branchings are covered by a layer of grey matter. If we suppose that one of the primary bmnches is composed of a certain number of laminm of fibrous matter, the se condary ramifications from it will in a great degree correspond. In most instances these secondary bmnches subdivide into two or more tertiary ones, which, as well as the branch from which they spring, are enclosed in grey matter. ( Figs. 380, 386.) A vertical section of the median lobe gives quite a similar appearance to that of the liernisphere.s. The central nucleus breaks up into primary branches,which become the centre of the lobules of which it consists. (Figs.386, 393.) The ramifications of the central nucleus, whether of the median lobe or of the hemi spheres, separate from it only in the vertical plane or from before backwards; in the latter direction, however, to a very slight extent. Bence these branches are directed only up wards, or downwards, or backwards. The fibrous matter of the median lobe is continuous, without any line of demarcation, with that of the hemispheric lobules. By reason of this disposition of the fibrous matter, the surface which is exposed by a horizontal section through the entire cerebellum, presents a very different appearance from that which results from a vertical section. It consists of a plane of fibrous matter bounded on the sides and behind by a narrow cortex of grey matter.