THE CEREBELLUM. 



1083 



studies (Stroud, Elliott Smith, Bradley, Bolk and others), since some details given 

 prominence in human anatomy are of secondary importance, and others of greater 

 morphological significance are only slightly emphasized. 



The surface of the cerebellum is divided by the deeper fissures into more or less 

 well defined areas, the lobules, each of which is subdivided by shallower clefts into 

 narrow tracts, the folia, from 2-4 mm. in width, that usually pursue a curved course 

 within a given lobule and, in a general way, run parallel to one another and to the 

 sulci bounding the tract. On separating the plate-like folia, or on making a section 

 across the plications (Fig. 943), it will be seen that the pattern of the folia is greatly 

 extended by the presence of numerous additional furrows on the deeper and hidden 

 aspects of the leaflets, which are, therefore, ordinarily invisible from the surface. 

 Whether free or sunken, the exterior of the cerebellum is everywhere formed by a 

 cortical layer (A gray matter, from 1-1.5 mm. thick, that encloses a viedullary layer 

 of white matter of variable thickness. Owing to this arrangement, sagittal sections 

 of the cerebellum expose an elaborate system of branching tracts of white and gray 

 matter, designated as the arbor vitcs (Fig. 938). 



The general ellipsoidal mass of the cerebellum, comprising the narrow central 

 vermis and the expanded lateral hemispheres, presents a superior and an inferior sur- 

 face and rounded anterior and posterior borders. Of these the anterior border is 

 indented by a wide groove, the anterior notch (incisura cerebelli anterior), which is 

 much larger than the posterior and bounded laterally by the cerebellar hemispheres 

 and behind by the anterior part of the worm. It is occupied by the inferior corpora 

 quadrigemina and the superior 



Fig. 938. 



Cerebral 

 peduncle 



Sylvian aqueduct 



Quadrigeminal plate 



Superior medullary velum 



Lobulus centralis 

 Lingula 



Culmen 



Core of white matter 



Tela chorioidea' 



Medulla 



Pyramis 



Uvula 



cerebellar peduncles and 

 intervening superior medul- 

 lary velum. The posterior 

 border is interrupted by a 

 smaller median indentation, 

 the posterior notch (incisura 

 cerebelli posterior), which is 

 bounded on each side by the 

 hemispheres and at the bottom 

 by the hind part of the worm, 

 and contains the crescentic 

 fold of dura known as the falx 

 cerebelli. 



The upper surface of 

 the cerebellum is modelled by 

 the overlying tentorium and 

 presents a slight median trans- 

 versely furrowed ridge that cor- 

 responds to the upper surface 

 of the middle division, orworm, 

 and is known as the vermis superior. The most elevated part of this surface lies 

 a short distance behind the anterior notch. From this point, designated the mon- 

 ticuhis, the upper surface slopes gradually downward on each side to the lateral 

 margins of the hemispheres, whilst it falls off more rapidly towards the posterior 

 notch. 



The lower surface of the cerebellum is much less regular, owing to the pres- 

 ence of a wide median groove, the vallecula, that is bordered laterally by the 

 rounded hemispheres and is continuous in front and behind with the anterior and 

 posterior notches. The bottom of the vallecula is occupied by the irregular ridge-like 

 surface of the middle lobe which is here known as the vermis inferior. The front 

 of the valley receives the dorsal surface of the medulla. 



The cerebellum is incompletely divided into an upper and a lower part by a deep 

 cleft, the great horizontal fissure (sulcus horizontalis cerebelli). The sulcus 

 begins in front, at the side of the middle cerebellar peduncle, by the junction of two 

 diverging limbs that embrace the three cerebellar peduncles. It passes usually con- 

 tinuously around the circumference of the cerebellum, but sometimes is interrupted 



Mesial sagittal section of brain-stem and cerebellum, showing fourth 

 ventricle, Sylvian aqueduct, and cerebellar worm. 



