FORM OF THE CEREBELLUM. 523 



alone exists ; and in most mammals it forms a central lobe very distinct from 

 the lateral portions. 



The hemispheres are separated behind by a deep notch. Superiorly, the 

 median portion or upper vermiform process, though slightly elevated, is not 

 marked off from the hemispheres, so that the general surface of the organ, 

 which is here inclined and flattened on each side, is uninterrupted. Below, 

 the hemispheres are convex, and are separated by a deep fossa, named the 

 vallecula, which is continuous with the notch behind, and in which the 

 inferior vermiform process lies concealed in a great measure by the sur- 

 rounding parts. Into this hollow the medulla oblongata is received in front, 

 and the falx cerebelli behind. 



Fig. 355. INFERIOR SURFACE OF THE CEREBELLUM WITH THE PONS VAROLII AND 

 MEDULLA OBLONQATA (from Sappey after Hirschfeld and Leveille.) f 



1, placed in the notch between the cerebellar hemispheres, is below the inferior 

 vermiform process ; 2, 2, median depression or vallecula ; 3, 3, 3, the biventral, slender, 

 and posterior inferior lobules of the hemisphere ; 4, the amygdala ; 5, flocculus or sub- 

 peduncular lobule ; 6, pons Varolii ; 7, its median groove ; 8, middle peduncle of the 

 cerebellum ; 9, medulla oblongata ; 10, 11, anterior part of the great horizontal fissure ; 

 12, 13, smaller and greater roots of the fifth pair of nerves; 14, sixth pair; 15, facial 

 nerve; 16, pars intermedia; 17, auditory nerve; 18, glosso-pharyngeal ; 19, pneuino- 

 gastric ; 20, spinal accessory; 21, hypoglossal nerve. 



The cerebellum, at the surface and for some depth, consists of numerous 

 nearly parallel laminse or folia, which are composed of grey and white 

 matter, and might be compared with the gyri of the cerebrum, but are 

 smaller and without convolution. These laminae are separated by slightly - 

 curved grooves or sulci of different depths. 



One principal fissure, or sulcus, named the great horizontal fissure, divides 

 the cerebellum into an upper and a lower portion. It begins in front at the 

 entrance of the middle peduncles, and passes horizontally backwards round 

 the outer border of the hemispheres. From this primary fissure, numerous 

 others proceed on both the upper and under surfaces, forming nearly parallel 

 curves, having their concavities turned forwards, and separating the folia from 

 each other. All these furrows do not go entirely round the hemisphere, for 

 many of them coalesce with one another ; and some of the smaller furrows 

 have even an oblique course between the others. Moreover, on opening the 



M M 2 



