NODULE AND FLOCCULUS. 75 



sagittal sections of .the worm on the lower part of the stalk of the tuber valvulse, 

 entirely concealed by the pyramid (see fig. 59 B). If this is the case, then the com- 

 bined slender and inferior semilunar lobes may be reckoned as collectively forming 

 a primary subdivision of the hemisphere, corresponding with the tuber posticum 

 of the worm and to which the term postero-inferior may be applied, 1 and the two 

 postero-inferior lobes, together with the tuber valvulae which unites them in the 

 middle line, may collectively be spoken of as the lobus tuberis. This large lobe 

 occupies at least two-thirds of the inferior surface of the cerebellum ; of the re 

 maining third more than one-half is occupied by the combined pyramid and biven- 

 tral lobes, about one-third by the uvula and amygdalae, and the small remaining 

 portion by the nodule and flocculus. 



Fissures of the under surface. The lobes of the under surface of the 

 organ are separated from one another by fissures extending deeply into both the 

 worm and hemispheres. In the worm there are three such interlobar depressions, 

 viz. : one between the nodule and the uvula (postnodular), one between the uvula 

 and pyramid (prepyr -amidol*), one between the pyramid and tuber valvulae (post- 

 pyramidal), besides the middle of the great horizontal fissure separating the tuber 

 valvulas from the folium cacuminis. In the hemispheres a larger number is 

 apparent. The postnodular sulcus passes laterally into a groove curved with its 

 convexity forwards which first limits the amygdala in front and then passes between 

 the flocculus and biventral lobe to join the anterior end of the great horizontal 

 fissure. The prepyramidal sulcus curves laterally round the outer side of the 

 amygdala^ separating it from the biventral lobe : it joins the postnodular in front 

 of the amygdala. From the sides of the postpyramidal sulcus three deep fissures, 

 concentric with one another, curve outwards and forwards over the under surface of 

 the hemisphere. The most anterior of these, and also the shortest, passes at first 

 more forwards, concealed by the amygdala before curving round in the manner 

 described. It lies between the biventral and slender lobes, and may be termed the 

 anterior arcuate or pregracile sulcus. The second of the three concentric fissures 

 subdivides the slender lobe into two nearly equal parts (lobulus gracilis anterior and 

 lobulus gracilis posterior) ; we may distinguish it as the middle arcuate or mid- 

 yracile. The third, which is the longest, separates the slender lobe from the 

 inferior semilunar lobe ; like the other two it arises at the mesial edge of the hemi- 

 sphere opposite the depression (postpyramidal sulcus) between the pyramid and the 

 tuber valvulae, and arches round on the lower surface of the hemisphere with its 

 concavity forward to fall into the great horizontal fissure at the antero-lateral margin. 

 This fissure may be termed the posterior arcuate or postgracile. Behind this 

 again there is a fairly well marked deep fissure, serving to subdivide the inferior 

 semilunar lobe. This may be termed the lower or lesser horizontal sulcus. Lastly, 

 the deep antero-posterior grooves which mark off the lower worm may conveniently 

 be termed the sulci valleculm (dexter et sinister). 



Lobes of the under surface. The lobes of the under surface of the organ 

 as already enumerated may be now more particularly described in order from before 

 back. 



The nodule and flocculus: lobus noduli. The nodule occupies much the 

 same position relatively to the inferior medullary velum and tent of the fourth 

 ventricle that the lingula occupies with regard to the superior medullary velum, but it 

 is usually better developed than the lingula. Although sometimes merely composed 

 of a few transverse laminae set upon the median part of the inferior medullary velum, 

 it more often appears as a distinct prominence having a separate branch of the 



1 In the previous edition of this work, the term postero-inferior was used as a synonym for the 

 inferior semilunar lobe. 



