THE HIND-BRAIN OR RHOMBENCEPHALON 



789 



tance into its substance, and divide it into a series of layers or leaves. The largest 

 and deepest fissure is named the horizontal sulcus. It commences in front of the 

 pons, and passes horizontally around the free margin of the hemisphere to the 

 middle line behind, and divides the cerebellum into an upper and a lower portion. 

 Several secondary but deep fissures separate the cerebellum into lobes, and these 

 are further subdivided by shallower sulci, which separate the individual folia or 

 laminae from each other. Sections across the laminae show that the folia, though 

 differing in appearance from the convolutions of the cerebrum, are analogous 

 to them, inasmuch as they consist of central white substance covered by gray 

 substance. 



The cerebellum is connected to the cerebrum, pons, and medulla oblongata; 

 the cerebrum by the superior peduncle, to the pons by the middle peduncle, 

 md to the medulla oblongata by the inferior peduncles. 



Ala lobuli centralis 

 Lobulus centralis * Postcentral 



Horizontal 

 sulcus 



Prceclival fissure 



Postclival 

 fissure 



FIG. 702. Upper surface of the cerebellum. (Schafer.) 



The upper surface of the cerebellum (Fig. 702) is elevated in the middle and sloped 

 toward the circumference, the hemispheres being connected together by the supe- 

 rior vermis, which assumes the form of a raised median ridge, most prominent 

 in front, but not sharply defined from the hemispheres. The superior vermis is 

 subdivided from before backward into the lingula, the lobulus centralis, the mon- 

 ticulus and the folium vermis, and each of these, with the exception of the lingula, 

 is continuous with the corresponding parts of the hemispheres the lobulus 

 centralis with the alas, the monticulus with the quadrangular lobules, and the 

 folium vermis with the superior semilunar lobules. 



The lingula (lingula cerebelli) is a small tongue-shaped process, consisting of 

 four or five folia; it lies in front of the lobulus centralis, and is concealed by it. 

 Anteriorly, it rests on the dorsal surface of the anterior medullary velum, and its 

 white substance is continuous with that of the velum. 



The Lobulus Centralis and Alas. The lobulus centralis is a small square lobule, 

 situated in the anterior cerebellar notch. It overlaps the lingula, from which it 



Sis separated by the precentral fissure; laterally, it extends along the upper and 

 anterior part of each hemisphere, where it forms a wing-like prolongation, the ala 

 lobuli centralis. 



The Monticulus and Quadrangular Lobules. The monticulus is the largest part 

 of the superior vermis. Anteriorly, it overlaps the lobulus centralis, from which 

 it is separated by the postcentral fissure ; laterally, it is continuous with the quad- 

 rangular lobule in the hemispheres. It is divided by the preclival fissure into an 



