THE BRAIN AND ITS MEMBRANES. 



729 



lobular fissure, it would appear that each group of three lobules would really con- 

 stitute a single lamina, or sheet, of white matter reaching from margin to margin 

 of the cerebellum, the central part (worm) being more prominent than the lateral 

 portions (hemispheres); while from each surface of this lamina would appear pro- 

 jecting ridges also of white matter, the entire lamina and ridges being covered by 



Tuber ralv. 



Culmen and 



Post. corp. / 

 auad. I 



nid 



quad. 



Sup. med. veL 



ffoduie 



FIG. 428. Antero-posterior median section of the worm. (Henle.) 



gray matter. The spaces between the ridges would be, of course, the intralobular 

 fissures. 



The Lingula and Fraenula. The lingula is the smallest lobule of the upper worm 

 {Figs. 428, 429, 430). It is peculiar from all the other lobules in that its cut 

 surface is not like a folium, but appears merely as a series of three or four 



Lob. centralit 



Pyramid 



/. ^7>;> 



Abdufe 

 FIG. 429. Antero-posterior median section of the worm, also showing fourth ventricle, X- (Gegenbaur.) 



small elevations on the dorsal surface of a layer of white matter (valve of 

 Vi-'U.itt'-ns). which is here emerging from the middle part of the great hori- 

 zontal fissure at the bottom of the anterior cerebellar notch. These elevations 

 are white matter (derived directly from the valve of Yieussens) covered by a 

 layer of gray matter which dips in between them. Posteriorly, this gray 

 matter is continuous with that of the central lobule; anteriorly, it disappears 

 or is continued merely as an epithelial layer over the dorsal surface of the valve 

 of Yieussens. 



The frcenula (Fig. 430) stretch laterally from each side of the lingula. They 

 are short, not reaching beyond the superior peduncles of the cerebellum, over 

 which they lie. Each fnenulum is overlapped considerably by the ala. 



Lobulus Centralis and Alae i Ficrs. 428. 429). The central lobule, though of good 

 size, is much smaller than the culmen. immediately behind, and by which it is 

 overlapped. It. in its turn, overlaps the lingula. and together with it forms the 

 bottom of the anterior notch. 



The airs are slender, and are prolonged almost to the lateral limits of the 

 anterior notch. Hence each is curved, with the concavity forward. 



Of the remaining lobules of the upper surface it may be noted that the culmen 



