CEREBELLUM. 601 



border. It is divided into three lobes: the lobulus centralis, a small lobe, 

 situated in the incisura anterior; the monticulus cerebelli, the central projecting 

 part of the process; and the commissure/, simplex, a small lobe near the incisura 

 posterior. 



The under surface of the cerebellum (Fig. 335) is subdivided into two lateral 

 hemispheres by a depression, the valley, which extends from before backwards 

 in the middle line. The lateral hemispheres are lodged in the inferior occipital 

 fossae; the median depression, or valley, receives the back part of the medulla 



Fig. 335. Under Surface of the Cerebellum. 



oblongata, is broader in the centre than at either extremity, and has, projecting 

 from its floor, part of the median lobe of the cerebellum, called the inferior 

 vermiform process. The parts entering into the composition of this body are, 

 from behind forwards, the commissura brevis, situated in the incisura posterior; 

 in front of this, a laminated conical projection, the pyramid; more anteriorly, a 

 larger eminence, the uvula, which is placed between the two rounded lobes 

 which occupy the sides of the valley, the amygdalae or tonsils, and is connected 

 with them by a commissure of gray matter, indented on the surface, called the 

 furrowed land. In front of the uvula is the nodule; it is the anterior pointed 

 termination of the inferior vermiform process, and projects into the cavity of 

 the fourth ventricle; it has been named by Malacarne the laminated tubercle. 

 On each side of the nodule is a thin layer of white substance, attached exter- 

 nally to the flocculus, and internally to the nodule; these form together the 

 posterior medullary velum, or commissure of the flocculus. It is usually covered 

 in and concealed by the amygdala, and cannot be seen until they are drawn 

 aside. This band is of a semilunar form on each side, its anterior margin being 

 free and concave, its posterior attached just in front of the furrowed band. 

 Between it and the nodulus and uvula behind, is a deep fossa, called the sival- 

 low's nest (nidus hirundinis). 



Lobes of the cerebellum. Each hemisphere is divided into an upper and a 

 lower portion by the great horizontal fissure, which commences in front at the 

 pons, and passes horizontally round the free margin of either hemisphere, 

 backwards to the middle line. From this primary fissure numerous secondary 

 fissures proceed, which separate the cerebellum into lobes. 



Upon the upper surface of either hemisphere there are two lobes, separated 

 from each other by a fissure. These are the anterior or square lobe, which 

 extends as far back as the posterior edge of the vermiform process, and the 

 posterior or semilunar lobe, which passes from the termination of the preceding 

 to the great horizontal fissure. 



Upon the under surface of either hemisphere there are five lobes, separated 

 by sulci; these are from before backwards; the flocculus or sub-peduncular lobe, 



