THE CEREBELLUM 



807 



(lingula vermis) will appear separated from the central lobule by the pre-central 

 sulcus. It is a thin, tongue-like anterior projection of the cortical substance 

 comprising four to eight folia adhering upon the anterior medullary velum, the roof 

 of the superior portion of the fourth ventricle. 



Inferior surface. — The three cerebellar peduncles of each side join to form a 

 single mass of white substance, and enter the ventral aspect of each hemisphere at 

 the medial and ventral extremity of the horizontal fissure. The inferior surface 

 of the cerebellum is less convex than the superior surface. The hemispheres are 

 decidedly separated by a continuation of the posterior cerebellar notch, which 

 becomes broader, the vallecula of the cerebellum, which contains the inferior 

 portion of the vermis, vermis inferior, and whose margins embrace the medulla 

 oblongata. The inferior surfaces of the hemispheres are each divided by the 

 intervening fissures into four lobes (fig. 636). 



Fig. 635. — Diagram of the Superior Surface of the Cerebellum. 



Cerebral peduncle 

 Substantia nigra 



Ala of central lobule 



Anterior sem 

 lunar lobe 



Posterior semi- 

 lunar lobe 



Superior semi- 

 lunar lobe 



Inferior quadrigeminate body 



Central lobule 



y fflTiy^ . Culmen of 



~ 7'^/ monticulus 



Inferior semi 

 lunar lobe 



Posterior cerebellar notch 



Declive of monticulus 

 Folium of vermis 



Below, the inferior semilunar lobe (postero-inferior lobe) is separated from the 

 superior semilunar lobe of the superior surface by the horizontal fissure. It is the 

 largest of the inferior lobes, and is broader at its medial extremity. Frequently 

 two and sometimes three of its curved sulci appear deeper than others, and sep- 

 arate it into two or three slender lobules [lobuli graciles]. More commonly there 

 are two of these, the lohulus gracilis -posterior and lohulus gracilis anterior, separated 

 by the postero-inferior sulcus. 



The biventral lobe is smaller and more curved than the inferior semilunar lobe, 

 from the anterior margin of which it is separated by the curved antero-inferior 

 sulcus. Its medial extremity is pointed and does not extend to the vermis; its 

 lateral extremity is broader and curves anteriorly to the ventral extremity of the 

 horizontal fissure — the line of outer termination of the inferior semilunar lobe. 



The tonsil [tonsilla cerebelli] (amygdala) is a rounded, triangular mass, placed 

 mesiallj' within the inner curvature of the biventral lobe, and separated from it 

 by the retrotonsillar fissure. Its inferior mesial border slightly overlaps the 

 vermis. 



The smallest of the lobes is the flocculus. It lies adjacent to the inferior and 

 lateral surface of the mass of white substance produced by the confluence of the 

 three cerebellar peduncles, and extends into the mesial extremity of the horizon- 

 tal fissure. It is so flattened that its short folia give it the appearance suggesting 

 its name. Occasionally there is added a second, less perfectly formed portion, 

 the secondary flocculus. From each floccular lobe there passes toward the mid- 

 line a thin band of white substance, the peduncle of the flocculus ; these extend 



